had worked) that the latter had been misled by Coccidian cysts and
spores, which he took for those of Lankesterella. The gametogony
and sporogony of Haemogregarina stepanovi in the leech agree in
essential particulars with the process above described. The microgametes
are extremely minute, and the sporozoites, which are
developed in the salivary glands, where the motile ookinetes finally
come to rest, are extremely “spirochaetiform”—the full
significance of this latter fact being, perhaps, not
appreciated.
Christophers recently described some remarkable phases which he regarded as belonging to the cycle of Haemogregarina gerbilli (one of the few Mammalian Haemogregarines known) in a louse (Haematopinus). In a private communication, however, the author states that he has probably mistaken phases in the development of an ordinary gregarine parasite in the louse for part of the life-cycle of this Haemogregarine.
The Mammalian parasite Piroplasma is the one about whose life-history our knowledge is most vague. Besides the typical and generally occurring forms, others have also been observed in the blood, but it is doubtful how far these are to be looked upon as normal; for instance, Bowhill and Le Doux have described, in various species, a phase in which a long, slender pseudopodial-like outgrowth is present, with a swelling at the distal end. It is, moreover, quite uncertain which are the sexual forms, comparable to gametocytes. Doflein regards large pear-shaped forms as such (megagametocytes?), which become spherical when maturing; and Nocard and Motas have figured amoeboid, irregular forms, with the nucleus fragmented and possessing flagella-like processes (possibly microgametes?). The Invertebrate host is well known to be, in the case of all species, a tick; thus bovine piroplasmosis (P. bigeminum) in America is conveyed by Rhipicephalus annulatus (Boophilus bovis), canine piroplasmosis (P. canis) in South Africa by Haemaphysalis leachi (and perhaps Dermacentor reticulatus), and so on. The manner in which the infection is transmitted by the tick varies greatly. In some cases (e.g. P. bigeminum and P. canis) only the generation subsequent to that which receives the infection (by feeding on an infected ox) can transmit it back again to another ox; in other words, true hereditary infection of the ova in the mother-tick is found to occur. The actual period in the life of the daughter-tick at which it can convey the infection apparently varies. On the other hand, in the case of East African coast-fever, Theiler found that hereditary infection does not occur, the same generation transmitting the parasite (P. parvum) at different periods of life. Little is certainly known regarding the phases of the parasite which are passed through in the tick. Lignières has observed a kind of multiple fission in the stomach, several very minute bodies, consisting mostly of chromatin, being formed, which may serve for endogenous reproduction. Koch has published an account of certain curious forms of P. bigeminum, in which the body is produced into many stiff, ray-like processes, giving the appearance of a star; according to him fusion of such forms takes place, and the resulting zygote becomes rounded, perhaps transitional to the pear-shaped forms.
The classification and nomenclature of the Haemosporidia are in a very unsettled condition. For an account of the various systems and modifications hitherto adopted, the article of Minchin (see under Sporozoa: Bibliography) should be consulted. With the realization that the life-history in the case of the Classification. “Haemamoebae” and the Haemogregarines is fundamentally similar in type, the chief reason for grouping them as distinct suborders has disappeared. It is most convenient to regard them as separate, but closely allied families, the Plasmodidae (“Haemamoebidae”) and the Haemogregarinidae. The Piroplasmata, on the other hand, constitute another family, which is better placed in a distinct section or sub-order. In addition there are, as already noted, two or three genera whose systematic position must be considered as quite uncertain. One is the well-known Halteridium of Labbé, parasitic in various birds; the type-species is H. danilewskyi (Gt. and Fel.). Another is the much-debated parasite of white blood-corpuscles (leucocytes), originally described in birds by Danilewsky under the name of Leucocytozoon, a form of which has been recently observed in Mammals.
In conclusion, the chief members of the above-mentioned families may be enumerated.
Fam. Plasmodidae (“Haemamoebidae”).
Genus Laverania, Gr. and Fel. (syn. Haemamoenas, Ross), for L. malariae, Gr. and Fel. (synn. L. s. Plasmodium, s. “Haemamoeba,” &c., praecox s. immaculatum, &c.), the parasite of pernicious malaria. Genus Plasmodium, March. and Celli (syn. “Haemamoeba”) for P. vivax and P. malariae, the tertian and quartan parasite, respectively. There is also a form known in apes, P. kochi. Genus Haemoproteus, Kruse (syn. Proteosoma), for H. danilewskyi (syn. Proteosoma grassi, Plasmodium praecox, &c.), parasitic in numerous birds. Recently, another form has been described, from reptiles, which Castellani and Willey have termed Haemocystidium simondi.
Remarks.—The distinguishing characters of the malarial parasites have been mentioned above. Some authorities would include Laverania in the genus Plasmodium, as differing only specifically from the other two forms. It has, moreover, been suggested by Sergent that all three are merely different phases of the same parasite, predominating at different seasons; this idea cannot be regarded, however, as in any way proved so far. From what is known of the morphology and mode of manifestation of these forms, the differences between Laverania and the two species of Plasmodium are considerably more pronounced than those between P. vivax and P. malariae; if the latter are to be considered as distinct species, the first-named is probably generically distinct. Lühe, it may be noted, in his recent comprehensive account of the Haematozoa, also takes this view. Lastly, whatever be the correct solution of the above problem, there is certainly not sufficient justification for including the Avian genus Haemoproteus, as also only a species of Plasmodium, which is done by some. Its different Vertebrate habitat, and also the fact that its Insectan definitive host is Culex and not Anopheles, differentiate it sharply from Laverania and Plasmodium.
|
| From Lankester’s Treatise on Zoology. |
| Fig. 5.—Haemoproteus danilewskyi, Kruse (parasite of various birds). × about 1200. a, b, c and f from the chaffinch; d and e from the lark. (After Labbé.) a, Young trophozoite in a blood-corpuscle, |
|
| From Lankester’s Treatise on Zoology. |
| Fig. 6.—Haemogregarina stepanovi, Danilewsky (par. Emys and Cistudo), phases of the schizogony. (a-e and j after Laveran; f-i after Börner.) × 1000 to 1200 diameters.
a, Blood-corpuscle with young trophozoite.
b, Older trophozoite. c, Full-grown trophozoite, ready to leave the corpuscle. d and e, Trophozoites free in the blood-plasma, showing changes of form. f-i, Trophozoites, still within the blood-corpuscle (not drawn), showing the structure of the nucleus, the coarse chromatoid granules in the protoplasm and the manner in which the parasite grows into the j, Commencement of sporulation; the nucleus has divided into eight nuclei, and the body of the parasite is beginning to divide up into as many merozoites within a blood-corpuscle. N, Nucleus of the blood-corpuscle. n, Nucleus of the parasite. |
Fam. Haemogregarinidae.—The different genera are characterized chiefly by their size relative to the blood-corpuscles, and their disposition in the latter. Here, again, it has been suggested to unite the various types all in one genus, Haemogregarina, but this seems at least premature when it is remembered how little is known in most cases of the life-cycle, which may prove to exhibit important divergences.
Genus Haemogregarina, Danilewsky (syn. Danilewskya, Labbé).
