vol. i.] Ritter- Davis. — Enteropneusta. is? 



activities are about at the lowest level to which it is possible for 

 them to be reduced and life still be maintained. 



The whole round of metabolic processes, including food- 

 taking, digestion, and assimilation, is in its simplest terms, it', 

 indeed, food-taking is not wholly wanting for a considerable part 

 of the time. The respiratory and excretory functions arc on the 

 simple protoplasmic level, there being not only no organ for 

 either function, but there is nothing to lead one to suppose thai 

 any one portion of either the ectoderm or the endoderm is better 

 fitted than any other for performing them. If there is anything 

 that can be counted as corresponding to the circulatory func- 

 tion, this certainly consists in nothing more than a stirring up 

 to a slight extent of the coeloblastic fluid, or semi-fluid, by the 

 slow rythmical contractions of a simple vesicle contained within 

 the fluid. 



The power of response to stimuli is at so low a level as to be 

 detected with difficulty by experiment. 



One function, namely, that of body movement, universally 

 recognized as one of the most characteristic marks of animal 

 life, is performed, but only on almost its lowest plane. It is not 

 by muscular, but by ciliary activity. 



Really, then, the problems of the life activities of this animal 

 are reduced almost exclusively to those of its body movements 

 These may be gotten at with a considerable measure of fullness, 

 and in what follows, while we are keenly aware that the subject 

 is not exhausted, we still feel that ground has been pretty well 

 broken . 



As has been pointed out in earlier pages, the eggs of this 

 species are pretty surely deposited on the sea bottom in consid- 

 erable depths of water. The larvae, on the contrary, are pelagic. 

 Two questions grow directly out of these facts: By what means 

 does the larva rise? What are the influences that cause it to rise"? 



Taking up these questions in order, we may give in a 

 single sentence our conclusions with reference to the first. The 

 larva rises partly through a reduction of its specific gravity, and 

 partly through swirhming by menus of its cilia. 



The facts relative to the specific gravity of the larva have been 

 ascertained by experiment. 



