12 SCHMIDT ON THE COMPARATIVE PHYSIOLOGY 



of large oily globules. This fat is fluid, of the consistence of 

 human fat, saponifiable by alkalies, and when heated is decom- 

 posed, evolving the characteristic odour of acroleine and a fatty 

 acid (thus containing oxide of glyceryle). The fatty acid, when 

 separated from the potash-soap, formed a brownish oil, which 

 when in solution reddened litmus, and yielded on analysis as 

 follows : — 



0"413 of the substance gave 1*150 carbonic acid and 0*4315 

 water; hence, — 



Carbon 76'03 per cent. 



Hydrogen .... 11-61 per cent. 

 i. e. very nearly the composition of oleic acid, so that there is no 

 further doubt about its nature. In the simplest animal forms 

 in which we are able to recognise the ovary anatomically with 

 certaint}', it is the only organ in which such abundance of fat 

 occurs accumulated in one spot ; we have therefore every reason 

 to regard Ehrenberg's idea as a well-founded observation. Fur- 

 ther remarks on the quantity of this fat (15 per cent.) in pro- 

 portion to the weight of the coats, the muscular substance and 

 the siliceous carapace, which is determinable with accuracy, also 

 on the manner of ascertaining it, will be found in connexion 

 with the cutaneous system. 



D. Vascular System. 

 The walls of the tubular conductors, as also the pulsating 

 central organ, appear, as regards chemical and in many respects 

 histological identity (layers of longitudinal and annular fibres), to 

 belong to the muscular system, and the former systems gene- 

 rally. The heart and its auricles, with the largest vascular trunks 

 of Unio, Anodonta, the Craw-fish, as also the dorsal vessel of 

 Squilla {mantis) and of Scolopendra {morsitans), reacted in the 

 same manner as regards solubility in alkalies, mere expansion 

 and acquiring transparency in acetic acid, burning with the dis- 

 agreeable odour of the albuminates, and becoming yellow by 

 nitric acid ; however, I could not make any elementary analysis 

 for want of sufficient substance. 



E. Respiratory System. 



In the animal series, as is known, to allow the exchange of the 

 gaseous products of the alteration of matter with the oxygen of 

 the atmosphere, we have external or internal sacs, in which, on 



