256 Dr. W. B. Benliam on a 



XXVI. — Note on a Couple of Ah normalities. 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 &. pair oi apertures on the 

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

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

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

 but that there are tioo oviducts on each side^ one passing into 

 the base of the Wtli appendage^ the other into that of the XZth 

 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 

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

 dages. 



It 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. novce 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 Lepas, amongst the Crustacea, Hoek (in ' Challenger ' 

 Re^jorts) 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 



