Fissiparous Species of Tuhicolar Annelid. 115 



Hermaphrodism has hitherto been observed in no errant or 

 tubicolar annelid.* Indeed the author to whom we are in- 

 debted for the most beautiful researches into annelid organiza- 

 tion extant, M. de Quatrefages, thus concludes his elaborate 

 memoir on the nervous system of the annelida : — 



" We must then seek elsewhere (than in the nervous sys- 

 tem) the characteristics on which to base the divisions which 

 are necessitated by the great extent of this group, and the 

 multiplicity of types which it embraces. Now, as an ana- 

 tomical character, there is nothing more distinct and well 

 marked than the union or separation of the sexes in the same 

 individual. These differences of organization, besides, indicate 

 profound physiological distinctions, which have long been justly 

 appreciated by botanists. I am, therefore, more and more 

 inclined to believe that the distinction of the annelids 

 (Vers) into monoecious and dioecious ought to be adopted in 

 science."t 



In arriving at this conclusion, M. de Quatrefages was, of 

 course, only furnishing additional evidence for the justice of 

 that division of the annelids into the Annelides proper, charac- 

 terized by the separation of their sexes — and the Scoleides, 

 characterized by their hermaphrodism — which was first esta- 

 blished by M. Milne-Edwards, and which has been very 

 generally received. 



However, on a careful survey of the whole class of worms, 

 many facts come to light which throw considerable doubt on 

 the propriety of raising unisexuality or hermaphrodism into 

 distinctive characters of large groups. We have hermaphro- 

 dite Rotifer a, and unisexual Rotifera. The Nemertidm and 

 Microstomum are unisexual, the other Turbellaria herma- 

 phrodite ; there appears to be considerable doubt as to the 

 universality of hermaphrodism in the Trematoda even ; and 

 Echinorhynchus , which cannot be placed very far from the 

 Tceniadm and Distomata, is well known to be unisexual, and 



* See among other authorities, Frey and Leuckart, op. cit. inf., p. 87, who exa- 

 mined Hermella, Vermilia, Fahricia, and Spirorbis, among the tubicolar anne- 

 lids, with especial reference to this point. 



t Types inferieurs del'Embranchement des Anneles. Ann, des Sc. Nat. 1850. 



h2 



