256 Dr. W. B. Benham on a 



XXVI. — Note on a Couple of Abnormalities. By W. 

 Blaxland Benham, D.Sc, University College, London. 



[Plate III.] 



Amongst the large number of crayfish (Astacus fluviatilis) 

 dissected annually in the zoological classes here I have noticed 

 from time to time certain abnormalities in regard to the genital 

 apertures in females, usually a doubling of the pore on one 

 side — that is, in addition to the normal pore on the base of the 

 11th appendage there is a second pore on that of the 12th. 



A short time ago (Nov. 24, 1890) one of my students drew 

 my attention to a female specimen, which, in addition to the 

 normal genital apertures, presented a pair of. apertures on the 

 bases of the 13th appendages, occupying, that is, the normal 

 position of the genital apertures of a male (see PL III. fig. 1). 

 On dissecting the specimen I find that the ovary is normal, 

 but that there are tivo oviducts on each side, one passing into 

 the base of the \lth appendage, the other into that of the 13th 

 appendage (see fig. 2) to the so-called " male pore." There 

 appears to be no trace of a testis and no evidence of an her- 

 maphrodite condition. The abdominal appendages are nor- 

 mally female. Taken in conjunction with the abnormalities 

 which I had already observed, this gives a possibility of a 

 pore and duct for each of the last three ambulatory appen- 

 dages. 



Jt is still a moot point whether genital ducts in the Arthro- 

 poda are derived from nephridia ; but there is some evidence 

 tending to support this idea. In Peripatus there is a pair of 

 nephridia in each of the leg-segments, except in the segment 

 containing the genital duct (in P. novas zelandice), which opens 

 in the same position as a nephridium and which GafFron has 

 shown possesses an " end-sac " similar to that of the nephridia. 

 In LepaSj amongst the Crustacea, Hoek (in ' Challenger ' 

 Reports) figures sections through the " segmental organ " 

 (" shell-gland ") of the 2nd maxillary segment, and through 

 the terminal portion of the oviduct, at the base of the next 

 appendage (first cirrhus), and points out the similarity 

 between them. In Nebalia the " shell-gland " of the 

 maxillary segment and the " green-gland " of the antennary 

 segment coexist (Claus, Arb. Zool. Inst. Wien, vol. viii. 

 1889) ; in other Crustacea one of these glands is present, 

 but not the other. 



These and other facts appear to point to the possession 

 originally by Arthropoda of a pair of segmental organs 



