104 MB. E. c. PFNNETT Ojst [May 21, 



which the relations of the vascular system on both these points • 

 are entirely wrong. At the same time the accoant given in the 

 text is erroneous. 



Note on a Secondary Sexual Character in a Nemertean. 



Hitherto no instance of an anatomical difference between the 

 sexes of any species of JN^emerfcean has been observed. Occasion- 

 ally during the breeding-season the male may be distinguished by 

 its colour from the female, but such differences are always directly 

 due to the hue of the gonads themselves. It has already been 

 mentioned (p. 92) that the number of proboscis-nerves in 

 A. tliomjpsoni is subject to considerable variation. Fourteen speci- 

 mens taken at random were sectioned, and the number of their 

 proboscis-nerves and their sex noted. From the subjoined table 

 it will be seen that the sexes are in almost equal proportions. 

 All were collected together from the same locality, all were of 

 about the same size, and all were sexually mature. 



No. of proboscis-nerves 10 11 12 13 14 15 16 17 18 



2 1 — 6 ______ 



6 __4----2 2 



Erom this it would appear that whilst the female has 12 

 nerves or less in the proboscis, the male has either 12 or else a 

 much greater number, i.e. 17 or 18, though this proboscis itself 

 was in all cases of about the same size. If a considerably greater 

 number could be examined with regard to these points, it is not 

 improbable that we should obtain for the male a bimodal curve, 

 such as has been described by Bateson and Brindley ^ in the case 

 of certain earwigs and beetles. It is interesting to notice that we 

 have here a case of sexual dimorphism where the organ affected is, 

 so far as we know, in no way concerned with sexual functions. 

 That the proboscis has nothing to do with copulation may be 

 gathered from Mcintosh's '^ interesting account of the deposition 

 of the ova and spermatozoa in an allied form — Eunemertes gracilis, 

 where the individuals of either sex did not approach within three 

 inches of one another, and fertilization took place in the surround- 

 sea-water. Into the possible raison cSetre of such a phenomenon 

 as this it seems at present useless to enquire. It is sufficient 

 here to draw to such facts the attention of those who propound 

 theories concerning secondary sexual characters. 



Develojiment of the Ovum in Drepanophorus borealis. 



That the ovary of Drepanophorus borealis contains eggs in 

 various stages has already been seen (p. 97). Throughout the 

 greater portion of the intestinal region the ovaries are large and 

 usually contain one almost or quite ripe ovum, and a number of 



1 Proc. Zool. Soc. 1892, p. 588. 

 ^ Loc. cit. p. 89. 



