CHAP. V.] 



HOMCEOSIS IN ARTHROPODA. 



153 



*85. After receiving these specimens I made an attempt to ascer- 

 tain the degree of frequency with which such variations occur in 



b.n 



ambM 



Right. 



Left. 



Fig. 20. Females of Astacus fluviatilis having an abnormal number of oviducal 

 openings. N.B. The form with three pairs of openings is not figured. 



A. Right oviducal opening absent. B. Extra opening in right penultimate 

 leg. C. Extra opening in left penultimate leg. 



the Crayfish, and though the total number examined is too small 

 to give a percentage of much value it may be well to record the 

 result. 



In all, 586 female A. fluviatilis have been examined : of these 

 563 were normal in respect of the number of oviducal openings, 

 and 23 were abnormal, as follows : 



1. Extra oviducal opening on left penult, leg 7 



2. ditto right 10 



3. ditto on both penult, legs 1 



4. ditto on both penult. & last legs 1 



5. Single oviducal opening on left side only 3 



6. ditto right 1 1 



Total abnormal specimens 2-'> 



1 Mr R. Assheton sends me word of a similar specimen found among 80 of both 

 sexes; Prof. W. B. Howes of another among 144 of both sexes. 



