1893.] PROSTATE IN THE OLIGOCH^TA. 485 



Eosa's view appears to me the most probable ; but this, how- 

 ever, he restricts to the GeoscoHcidse. In certain Geoscolicidae, 

 for example iii JlicrocJueta beahami, there are a series of paired 

 glands in the neighbourhood of the male pores ; in some species, for 

 example in Kynotus hdcliadsenii, setae are associated with these 

 glands which are in all respects similar to the penial setae of other 

 Earthworms. His view is that one pair of the glands have become 

 converted into the " pseudoprostates " of other Geoscolicidae, 

 which I regard, as already pointed out, as identical with the atria 

 of other Oligochaeta. These glands are identical in structure with 

 atria, and theoretical con-iiderations also favour their homology. 

 There are many instances amoug segmented animals of the re- 

 duction or concentration of metamerically repeated organs ; we are 

 more likely to be correct in assuming in such cases a reduction than 

 a multiplication. It is easy on this assumption to understand the 

 complete independence in the Acanthodrilidae of the sperm-ducts and 

 the atria ; and, furthermore, the remains of additional glands such as 

 occur in Dichogaster damonis ; in this worm there are three pairs 

 of tubular glands of which one only is connected with the sperm- 

 duct. It is even possible that the glands (which I have called 

 " capsulogenous ") of the Perichaetidae are referable to the same 

 category ; and it may be pointed out that the papillae upon which 

 they open are sometimes regularly paired and correspond more or 

 less accurately in position to the male pores. On this hypothesis 

 of the original development of the atria out of copulatory glands, 

 it is clear that those of the higher Ohgochaeta are nearer to the 

 primitive form of these glands than the lower ; and, furthermore, 

 that the retention of more than one pair and their independence 

 of the sperm-ducts are so far primitive characters. The Acantho- 

 drUidae conae obviously very near to the base of the series, though 

 a little further off then certain of the GeoscoHcidae. The Peri- 

 chaetidae and the Cryptodrilidae can readily be derived from the 

 Acanthodrilidae, and it must be remembered that some of the 

 former have tubular atria and may therefore be nearer to the 

 ground form. I do not propose in fact to discuss the relative 

 positions of the different families, as I should have to take other 

 characters into consideration with which this paper does not deal. 



The question of terminology has now to be considered ; it 

 evidently stands in need of revision. Are we to retain the terms 

 " atrium " and " prostate," or one or neither ? They have been 

 used in so many senses that it will lead to misunderstanding if 

 they are again used without careful definition. The use of the 

 term atrium has the objections that Mr. Benham has urged ; for in 

 Acanthodrilus, for example, the atrium is not a chamber leading 

 into any other chamber or duct ; on the other hand, to speak of 

 the " atrium " of Tuhifex as a " prostate " would give a wrong 

 impression, for the idea of a prostate is a glandular appendix to 

 the male ducts. To speak of the sac itself as an atrium and of 

 the coating of pear-shaped cells as the prostate is disadvantageous ; 

 for, excepting in Tuhifex, the two parts of the terminal apparatus 



Pkoc. Zool. ttoc— 1893, Xo. XXXIII. 33 



