Page:An Introduction to the Study of Fishes.djvu/91

 

CHAPTER IV.

MODIFICATIONS OF THE SKELETON.

The lowermost sub-class of fishes, which comprises one form only, the Lancelet (Branchiostoma [s. Amphioxus] lanceolatum, possesses the skeleton of the most primitive type.

Fig. 28.—Branchiostoma lanceolatum.
a, Mouth; b, Vent; c, abdominal porus.

Fig. 29.—Anterior end of body of Branchiostoma (magn.)
d, Chorda dorsalis; e, Spinal chord; f, Cartilaginous rods; g, Eye;
h, Branchial rods; i, Labial cartilage; k, Oral cirrhi.

The vertebral column is represented by a simple chorda dorsalis or notochord only, which extends from one extremity of the fish to the other, and, so far from being expanded into