38 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



rings. Mantle thick. Alternation 

 of generations simple, solitary- 

 asexual individuals alternating 

 with a chain-like series of sexual 

 forms. X Salpa. 



Class III. LEPTOCARDII This class contains a very few 



closely allied animals, of which 

 Branchiosioma (= Amphioxus) is 

 the typical representative. The 

 body is fish-like, but without defi- 

 nite head, and pointed at both 

 ends. The notochord extends 

 through the entire body, from tip 

 to tip, just dorsal to the aliment- 

 ary canal. The pharynx is per- 

 forated by numerous pairs of lateral 

 gill-slits, which in the larva com- 

 municate directly with the exterior, 

 but which in the adult open into 

 a spacious peribranchial chamber 

 formed by folds of the integument 

 and communicating with the ex- 

 terior by means of a median ventral 

 opening, the atriopo're, situated 

 posteriorly, but anterior to the 

 anus. The central nervous sys- 

 tem consists of a dorsal cord 

 lying upon the notochord. In 

 general plan of structure and the 

 relationship of the organs these 

 animals are essentially Vertebrate, 

 but they lack a definite head, and 

 are without skull or specially 

 differentiated brain. 



X Branchiostoma. 



