AMPHIOXUS — AMPTHILL features of interest, and cannot fail to retain its importance as an introduction to the study of embryology. The four principal phases in the development are: (1) Blastula, (2) Gastrula, (3) Flagellate Embryo, (4) Larva. The segmentation or cleavage of the ovum which follows upon fertilization terminates in the achievement of the blastula form, a minute sphere of cells surrounding a central cavity. Then follows the phenomenon of gastrulation, by which one-half of the blastula is invaginated into the other, so as to obliterate the segmentation cavity. The embryo now consists of two layers of cells, epiblast and hypoblast, surrounding a cavity, the archenteron, which opens to the exterior by the orifice of invagination or blastopore. One important fact should be noted with regard to the gastrula, in which it seems to differ from the gastrulse of invertebrata. After invagination is completed, the embryo begins to elongate, the blastopore becomes narrower, and the dorsal wall of the gastrula loses its convexity and becomes flattened to form the dorsal plate, the outer layer of which is the primordium of the neurochord, and the inner layer the primordium of the notochord. While still within the egg-membrane the epiblastic cells become flagellated, and the gastrula rotates within the membrane. About the eighth hour after commencement of development the membrane ruptures and the oval embryo escapes, swimming by means of its flagella at the surface of the sea for another twenty-four hours, during which the principal organs are laid down, although the mouth does not open until the close
Pxq. 4. Anterior region of two pelagic larvse of A. lanceolatus obtained by the tow-net in 8-10 fathoms, showing the asymmetry of the large lateral sinistral mouth with its ciliated margin cm and the dextral series of simple primary gill-slits (ps-lips). The larvee swim normally like the adult or suspend themselves by their flagella (not shown in the figures) vertically in midwater. There is nothing in their mode of life which will afford an explanation of the asymmetry which is a developmental phenomenon. Lettering of upper figure.—anp, anterior neural pore ; be, rudiment of buccal skeleton ; c, cilia; cb, ciliated band ; cc, ciliated groove ; cm, cilia at margin of mouth ; gl external opening of club-shaped gland ; Hn, Hatschek’s nephridium ; Im, left metapleur; n, notochord ; pp, prseoral pit; ps, primary gill-slits, 1, 5, and 13 ; rm, right metapleur showing through. Lettering of lower figure.— a, atrium ; al, alimentary canal; bv, blood-vessel; cv, cerebral vesicle ; df, dorsal section of myoccel (=fin-spaces); e, “eyespot”; end, endostyle ; gl club-shaped gland ; Im, edge of left metapleur ; m, lower edge of mouth ; n! notochord ; nt, pigmented nerve tube ; ps, primary gill-slits, 1, 9, and 14 ; rc, renal cells on atrial floor ; rm, edge of right metapleur ; so, sense organ opening into prseoral pit; ss, thickenings, the rudiments of the row of secondary gill-slits. of this period. The primordium of the neurochord (neural or medullary plate) referred to above becomes closed in from the surface by the overgrowth of surrounding epiblast, and its edges also bend up, meet, and finally fuse to form a tube, the medullary or neural tube. An important fact to note is that the blastopore is included in this overgrowth of epiblast, so that the neural tube remains for some time in open communication with the archenteron by means of a posterior neurenteric canal. It is still longer before the neural tube completes its closure in front, exhibiting a small orifice at the surface, the anterior neuropore. It is thus possible that the neurenteric canal is due to the conjunction of a posterior neuropore with the blastopore, i.e., it is a complex and not a simple structure. Paired archenteric pouches meanwhile appear at the sides of the axial notochordal tract, the mesoblastic somites. The first of these differs in several respects from those which succeed, and has been called the collar cavity (MacBride). In front of the latter there remains a portion of the archenteron, which becomes constricted off as the head cavity. This becomes divided into two, the right half forming the cavity of the rostrum, while the left acquires an opening to the exterior, and forms the prceoral pit of the larva, which subsequently gives rise to special ciliated tracts in the vestibule of the mouth mentioned above. The larval period commences at about the thirty-sixth hour with the perforation of the mouth, first gill-cleft, and anus. The larva is curiously asymmetrical, as many as fourteen gill-clefts appearing
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in an unpaired series on the right side, while the mouth is a large orifice on the left side, the anus being median. The adult form is achieved by metamorphosis, which cannot be further described here. One point must not be omitted, namely, the homogeny of the endostyle of A. and the thyroid gland ot Craniota. References.—Boveri. “DieNierencanalchendesAmphioxus, Zool. Jahrb. Anat, v. 1892, p. 429.—Felix. “ Beitrage zur Entwickelungsgeschichte der Salmoniden,” Anat. Hefte Arb. viii. 1897 ; Amphioxus, p. 333.—Garbowski. u Amphioxus &s Grundlage der Mesodermtheorie,” Anat. Anz. xiv. 1898, p. 473. —Hesse. “Die Sehorgane des Amphioxus,’’ Zeitschr. wiss. Zool. Ixiii. 1898, p. 456.—Kikkaldy. “A Revision of the Genera and Species of the Branchiostomidae,” Quart. J. Micr. Sci. xxxvii. 1895, p. 303.—Lankester. “Contributions to the Knowledge of Amphioxus lanceolatus (Yarrell),” op. cit., xxix. 1889, p. 365. —Lwoff. “Die Bildung der primaren Keimblatter und die Entstehung der Chorda und des Mesoderms bei den Wirbelthieren,” Bull. Soc. Moscow, 1894.—MacBride. “The early_ Development of Amphioxtcs,” Quart. J. Micr. Sci. xl. 1897, p_. 589, and xliii. 1900.—Morgan and Hazen. “The Gastrulation of Amphioxus,” J. Morphol. xvi. 1900, p. 569. — Sammassa. “Studien fiber den Einfluss des Dotters auf die Gastrulation und die Bildung der primaren Keimblatter der Wirbelthiere: iv. Amphioxus,” Arch. Entwickmech. vii. 1898, p. 1.—Schneider. “Einiges fiber Resorption und Excretion bei Amphioxus lanceolatus” Anat. Anz. xvi. 1900, p. 60-1.—Sobotta. “Die Reifung und Befruchtung des Eies von Amphioxus lanceolatus,” Arch, mikr. Anat. 1. 1897, p. 15.—Weiss. “Excretory tubules in Amphioxus lanceolatus,” Quart. J. Micr. Sci. xxxi. 1890, p. 489. —Willey. Amphioxus and the Ancestry of the Vertebrates, 1894 ; “Remarks on some recent Work on the Protochorda,” Quart. J. Micr. Sci. xlii. 1899, p. 223; “ Dolichorhynchus indicus,” ibid., 1901.—Benham. “ Heteropleuron of New Zealand,” ibid., 1901. —Burchardt. “ Finer Anatomy of Amphioxus,” with bibliography, Jena Zeitschr. xxxiv. 1900, p. 719. (a. W.*) AmpthiSI, Odo William Leopold Russell, 1st Baron (1829-1884), British diplomatist and ambassador, was born in Florence on the 20th of February 1829. He was the son of Major-General Lord George William Russell, by Elizabeth Ann, niece of the marquess of Hastings, who was governor-general during the final struggle with the Mahrattas. His education, like that of his two brothers — Hastings, who became eventually ninth duke of Bedford, and Arthur, who sat for a generation in the House of Commons as member for Tavistock—was carried on entirely at home, under the general direction of his mother, whose beauty was celebrated by Byron in Beppo. Lady William Russell was as strongwilled as she was beautiful, and certainly deserved to be described as she was by Disraeli, who said in conversation, “ I think she is the most fortunate woman in England, for she has the three nicest sons.” If it had not been for her strong will it is as likely as not that all the three would have gone through the usual mill of a public school, and have lost half their very peculiar charm. In March 1849 Odo was appointed by Lord Malmesbury attache at Vienna. From 1850 to 1852 he was temporarily employed in the Foreign Office, whence he passed to Paris. He remained there, however, only about two months, when he was transferred to Vienna. In 1853 he became second paid attache at Paris, and in August 1854 he was transferred as first paid attache to Constantinople, where he served under Lord Stratford de Redclifie. He had charge of the embassy during his chief’s two visits to the Crimea in 1855, but left the east to work under Lord Napier at Washington in 1857. In the following year he became secretary of legation at Florence, but was detached from that place to reside in Rome, where he remained for twelve years, till August 1870. During all that period he was the real though unofficial representative of England at the Vatican, and his consummate tact enabled him to do all, and more than all, that an ordinary man could have done in a stronger position. A reference, however, to his evidence before a committee of the House of Commons in 1871 will make it clear to any unprejudiced reader that
