140 Proceedings of the Royal Physical Society. 



GENITAL APERTURES. 



A normal male Nephrops norvegicus has two genital apertures, one on 

 each of the fifth pair of walking legs, while in the female the openings are on 

 the third pair. Of the 2064 individuals here dealt with, 1775 males and 76 

 females showed the typical arrangement of spermatic and oviducal openings. 

 In the remaining examples, the following abnormalities in the genital pores 

 were noted among the males : 



(1) 1 individual had 1 genital opening. 



(2) 154 individuals had 3 „ openings. 

 (6) 45 ,, „ 4 „ ,, 



(4) 10 „ „ 5 „ 



(5) 6 „ „ b „ „ 



1. Example with One Genital Opening. 



In a previous communication on this subject, I remarked 1 that " the 

 abnormality consists in the occurrence of additional genital apertures, for in 

 no case were the normal ones awanting " (I.e. p. 140). This statement must 

 now be modified. So far as I have been able to ascertain, this is the first 

 recorded case of a male with a single genital aperture, and that such an 

 individual is of rare occurrence, is shown by the fact that only one was 

 found among over 8000 individuals which have been specifically examined. 

 The single opening occurred on the fifth right leg; the fifth left leg, 

 while being otherwise normal, had no genital aperture. This individual is 

 well-grown, and is now preserved in Edinburgh University Zoological 

 Laboratory. 2 In the case of Astacus fluviatilis, while there is no record, so 

 far as I can find, of examples with any additional spermatic apertures, 

 Bateson 3 says : " Of 714 males examined, only one was abnormal, having no 

 trace of a genital opening on the right side, the vas deferens ending blindly 

 and hanging free in the thoracic cavity." Dr J. H. Ashworth of the Zoological 

 Department of Edinburgh University has kindly shown me an example in 

 his possession, with an identical external abnormality.' 1 Bateson also gives 

 the results of the examination of 586 female A. fluviatilis : " Of these, 563 were 

 normal, in respect to the number of oviducal openings, and 23 were abnormal" 

 (I.e., p. 153). Of the 23 abnormal specimens, 19 showed an excess of ovi- 

 ducal openings, and of the remaining 4 individuals, " 3 had a single oviducal 

 opening on the left side only, and one had a single oviducal opening on the 

 right side" (I.e., p. 153). 



1 M'lutosh, I). C, I.e., p. 140. 3 Bateson, op. cit,., p. 154. 



2 This specimen was exhibited at the meeting. * This specimen was also exhibited. 



