t>f Invertebrate. Animals. ' " 379 



Tlic cloaca on the abdominal purtacc of the body is small and 

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

 Serpentaria. The anterior extremities of the ovaries, or all tljat 

 lies in the continuous portion of the common ca\nty, arc very 

 sliirhtly attached ; that again which belongs to the intcrrapted 

 portion of the cavity is more firmly bound down. ' ' 



In the most perfect specimen 1 could obtain the posterior ex- 

 tremity was bifurcated, but the oj)ening in it was so large that it 

 appeared to be only in process of tillhig up aftei* 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 froni the above descri])tions 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 

 s])ecies it would appear to be common to the rcspiratoiy, 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 Sn-pentaria it acts I 

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

 pur])ose its construction is slightly different fi-om that of Ne- 

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

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

 tnnu])ct-shaped proboscis, which is continuous with a large ]mck- 

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

 connnon cavity, and which, contrary to the supposition of Kathkc 

 and other natui-alists, is, according to the opinion already expressed 

 by Ehrenberg, tlie 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 ft'om 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 Serpent aria this is more fully 

 shown than in Nemertes. In the former the ova arc apj^arently 

 develo])ed 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. i .v.no\ 

 Quatrefages and others suppose that the slender filsftnbnts 

 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 are so highly organized as to have a nervous STstcm, 



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