152 MERISTIC VARIATION. [part i. 



Variation in the number of generative openings in Crayfishes. 



Astacus fluviatilis. A female having the normal pair of 

 oviducal openings on the bases of the antepenultimate pair of 

 walking legs, and in addition to them another pair of similar 

 openings placed upon the corresponding joints of the penultimate 

 pair of walking legs. On dissection it was found that the ovary 

 was normal, and that from each side of it a normal oviduct was 

 given off; but each of these oviducts divided a little lower down 

 to form two smaller oviducts, one of which went to each of the 

 four oviducal openings. Desmarest 1 , E., Ann. Soc. Ent. France, 

 1848, Ser. 2, vi. p. 479, PI. 



Astacus fluviatilis $ , having a supernumerary pair of ovi- 

 ducal openings placed on the last pair of thoracic legs. The normal 

 oviducal openings were in the usual position and of the usual 

 shape and size, but in addition to them there was an extra pair 

 placed on the last thoracic legs. It should be remarked that 

 though these are the appendages upon which the openings of the 

 male organs are placed, the oviducal openings were not in this 

 case situated at the posterior surface of the joint as the male 

 openings are, but were placed relatively to the leg in the same 

 situation as the female openings on the antepenultimate legs. The 

 penultimate legs and the abdominal appendages were normal. On 

 dissection it was found that each oviduct after passing for the 

 greater part of its course as a single tube, divided into two parts, 

 one of which went to each oviducal opening. The ovary itself 

 was normal. Benham, W. B., Ann. Mag. N.H., 1891, Ser. 6, vn. 

 p. 256, PI. ill. fl am greatly obliged to Mr Benham for an oppor- 

 tunity of examining this specimen. Attention is called to the 

 fact that in this specimen Homoeosis occurs in an unusual way, 

 leaving a gap in the series ; for the openings are on the ante- 

 penultimate and last thoracic legs respectively.] 



Desmarest's observation stood apparently alone until lately, when 

 the specimen just described and several others presenting the same 

 or similar variations were observed by Benham. Mr Benham was 



%J 



kind enough to send me the following specimens for examination : 

 one female having a single extra oviducal opening on the left side 

 upon the penultimate thoracic leg (Fig. 20 C), and two females 

 having a similar extra opening in the same place on the right 

 (Fig. 20, B) ; in both of these the normal oviducal openings were 

 unchanged. Together with these Mr Benham also sent a female 

 having only one oviducal opening on the right side and another 

 having only the left oviducal opening (Fig. 20, A), the correspond- 

 ing leg of the other side having no trace of an opening. 



1 Desmarest had this specimen from Rousseau {I. c, p. 481 note): Faxon 

 quoting the case (Harv. Bull., viii.) accidentally represents it as two cases, but the 

 note to Desmarest's paper shews that the description referred to a single specimen 

 only. 



