1890.] Development of the Atrial Chamber of Ampliioxus. 



Kowalewsky says that after a certain number of gill-slits have 

 been formed two longitudinal folds appear on opposite sides of the 

 body, which grow rouud and meet, and finally fuse together in the 

 median ventral line, leaving a wide aperture at one end the atrio- 

 pore. His figures, two of which are hero reproduced (figs. 1 and 2j, 



FIG. 1. 



FIG. 2. 



Conies of Kowalewsky's figures of transverse sections through a larva of 

 A mphioxus with fully-formed atrium. Fig. 1 represents a section taken between 

 pharynx and atriopore ; and fig. 2, one taken just behind the atriopore of the same 

 larva. 



Int. Intestine. at. Atrium. l.h. Coelotn. 



bear this description put, more or less, while Rolph's schematic 

 figures bear it out entirely. The latter fire reproduced in figs. 3, 4, 

 and 5. 



FIG. 3. 



Lh 



Copy of Eolph's theoretical section through the pharyngeal region of a larva, 

 before the commencement of the so-called epipleural folds. 

 N. Nerve-cord. Ch. Notochord. 



M. Muscles. l.h. Coelom. 



1). Intestine. a. Intestinal epithelium. 



l>. Epidermis. 



G 2 



