COMPARATIVE ANATOMY. 37 



species, of great distention owing to the large blood sinuses contained within. 

 Between the ridges the hning of the atrium is developed into simple or branched, 

 finger-like processes termed cirri. Each is composed of glanchdar and sensory 

 cells frequently pigmented, and is penetrated by a slender canal traversed by a 

 nerve fibre. Regarding the function of these organs and the ridges it is vari- 

 ously considered that they are gustatory, olfactory or tactile, or even respiratory. 

 The cirri may be protruded from the opening, and this fact in connection with 

 their glandular character has suggested that they may serve also to collect food; 

 but judging from Drepanomcaia vaiupyrella (page 79) there are times when they 

 are inoperative in this respect. 



Regarding the papillae in the hypodermis of the Neomeniina various 

 hypotheses have been suggested. They appear to be connected with nerve 

 fibres, and may reasonably be considered the homologue of the aesthetes in 

 the shell of the Chitons, but up to the present time there is no proof that such 

 is the case, nor that they are tactile, or secretory, or excretory, organs as some 

 authors have maintained. 



A sul>i-adular organ, normally located and innervated, is known to exist 

 in a few species (page 86). In its finer details it bears a striking resemblance to 

 its homologue in the Chitons and perhaps functions in the same way. 



CoELOM. — The secondary body cavity comprises the gonad, pericardium, 

 and gonoducts whose relations have been determined in most of the known 

 species of Solenogastres although their physiological significance remains very 

 incomplete. The gonad, usually paired, is situated along the dorsal side of the 

 animal between the body wall and alimentary canal. Posteriorly it is continu- 

 ous, by means of two ducts, with the pericardium which in turn is in communica- 

 tion with the cloacal cavity by means of two canals, the coelomoducts. 



vSo far as known all the Chaetodermatina are dioecious while the Neomeniina 

 are hermaphroditic, and generally speaking the gonad is of the same length as 

 the liver and therefore nearly as long as the body in members of the first named 

 suborder. In the young the reproductive gland is paired, and in the adults with 

 the exception of the genus Chaetoderma this condition of affairs persists, though 

 sometimes jmrtially obscured by the development of numerous germinal folds. 

 In the Neomeniina the sperms arise along the outer walls of the gland while 

 the ova, in some species surrounded by a follicle, are more inwardly placed. 

 In the mature state the ova and spermatozoa make their way through the short, 

 ciliated canals terminating the gonad posteriorly, and enter the pericardium 

 from whence they pass to the outside through coelomoducts of various degrees 



