176 University of California Publication*. [zoology. 



smaller ones being situated ou both sides of these. The arrange- 

 ment is shown in a diagrammatic representation of a cross section 

 of the band in PI. XIX. Fig. 15, and the size of these as com- 

 pared with the cilia of the tentacles is shown in PI. XIX, Fig. 

 14. In the living, active larva the movement of the large cilia 

 quite obscures that of the small ones. 



When the larva is subjected to narcotization with chloretone 

 the movements of the cilia are no longer metachronous, and 

 under these conditions the two sizes may be readily observed. 

 They may also be seen on dying animals, and upon fragments of 

 the band held under compression. The presence of these two 

 sizes of cilia in the girdle seems to have escaped the notice of 

 previous observers, though Morgan, '94, mentions the presence 

 of a line of deeply stained nuclei behind the band that "I should 

 expect to carry cilia during life." 



From the physiological point of view the most interesting 

 internal characteristics of the larva are the blastocoel and its 

 contents, and the intestinal tract, the stomach in particular. 

 The great size of the blastocoel cavity, even in comparison with 

 the inflated stomach of all species of tornaria, is a familiar fact 

 to all who have examined either the animals themselves or the 

 figures published by various writers. The following measure- 

 ments of a typical specimen of T. ritteri, together with a refer- 

 ence to PI. XVII, Fig. 1, will serve to remind the reader of the 

 relations under consideration: Diameter of the animal as a whole. 

 1.99 mm.; diameter of the stomach, 1.08 mm. From this it is 

 seen that .91mm., or nearly forty-six per cent, of the entire 

 diameter of the animal is blastocoel space. Or, stated in terms 

 of cubic contents, which of course is the more significant, we 

 find that, in the same specimen, assuming both intestinal tract 

 and the larva as a whole to be cylinders, the first situated 

 within, and concenti'ic with, the second, the blastocoel space is 

 about eighty-four per cent, of the whole. As a matter of fact, 

 however, the proportion would actually be greater, since the 

 intestinal tract departs more from the assumed cylinder than 

 does the body as a whole, both of its ends being much smaller 

 relatively in diameter than is the stomach. A blastocoel space 

 occupying ninety per cent, of the total volume of the animal is 



