of Invertebrate Animals. 379 



The cloaca on the abdominal surface of the body is small and 

 rounded, and opens into an oblong cavity similar to that of 

 Serpent aria. The anterior extremities of the ovaries, or all that 

 lies in the continuous portion of the common cavity, are very 

 slightly attached ; that again which belongs to the interrupted 

 portion of the cavity is more firmly bound down. 



In the most perfect specimen I could obtain the posterior ex- 

 tremity was bifurcated, but the opening in it was so large that it 

 appeared to be only in process of filling up after the last separa- 

 tion, and therefore in all probability was not perfect. 



The leading features in the structure of both of these animals 

 will be seen from the above descriptions to be similar. Owing to 

 the assistance derived from the comparison of the two, I think I 

 have been enabled to make out more satisfactorily than has been 

 hitherto done, the true structure of Nemertes and its congeners. 

 To begin with the large common cavity of the body, in both 

 species it would appear to be common to the respiratory, diges- 

 tive, and at the same time to the generative systems. The water 

 in which the animal lives is transmitted through this cavity, and 

 thus acts as a means of respiration. In Serpent aria it acts I 

 would say almost altogether as an organ of digestion, and for this 

 purpose its construction is slightly different from that of iVe- 

 mertes, in which animal the structure approaches more to that of 

 the true Planaria, in so far as it is endowed with an extensile 

 trumpet-shaped proboscis, which is continuous with a large puck- 

 ered-up tube running along the upper and central part of the 

 common cavity, and which, contrary to the supposition of Rathke 

 and other naturalists, is, according to the opinion already expressed 

 by Ehrenberg, the intestinal canal. It is tied down at intervals by 

 a strong fibrous or muscular band — mesentery, which, when un- 

 wound, allows the intestine to escape from its attachments. The 

 ovaries which run down on each side of the body have no means 

 of throwing off the ova except into the common cavity. It ap- 

 pears to me therefore that Ehrenberg is correct in supposing that 

 cavity to be an egg-passage, and in Serpentaria this is more fully 

 shown than in Nemertes. In the former the ova are apparently 

 developed throughout the whole length of the ovaries, so that they 

 have no way of escaping except by means of the common cavity ; 

 in the latter the ova are only being fully developed at the poste- 

 rior extremity of the ovaries. 



Quatrefages and others suppose that the slender filaments 

 which run along each side of the body belong to the nervous 

 system, but from all the observations I have made, there cannot 

 be a doubt that they are the testicles of the animal ; besides, we 

 are bound by analogy to infer that none of the animals belonging 

 to this order arc so highly organized as to have a nervous system, 



2D2 



