98 



W. J. CROZIER AND L. H. SNYDEK. 



are closely similar. A like explanation holds for the selective pair- 

 ing of the nudibranch Clironwdons zebra (Crozier, 1918, 1920) ; 

 and perhaps also in the case of Leptinotarsa, although here Tower's 

 (1906, pp. 238-243) account of the matter is not at all clear. At- 

 tempts to discover selective breeding involving other than size 

 characters, among insects for example, have not been very suc- 

 cessful. Kellogg (1906) describes observations upon 54 matings 

 of Hippodamia, interpreted by him to signify that with respect to 

 color pattern pairing is entirely at random. As Pearl (i9O/ 6 ) 

 remarks in a review of Kellogg's note, the observations, on the 

 contrary, actually do indicate possible assortment. 



For preliminary study of pairing in forms possible to breed in 

 the laboratory, we have examined naturally occurring couples ran- 

 domly taken of two species of Gammarids-: Gaminanis locusta 

 (Linn.) and Dikerogannn&rus fasciatus (Say). Sixty-one pairs 

 of Ganimarus were obtained from one spot on the Staten Island 

 shore of Raritan Bay; and seventy-one of Dikcrogammarns were 

 taken from the Raritan River at a point about a mile above New 

 Brunswick. 



It is possible to study size relations of members of the breeding 

 pairs because the female is carried about by the male for a con- 

 siderable time, fecundation occurring after an ecdysis by the fe- 



mm. 



12 

 1 1 

 10 



9 

 8 



7 



6 



5 

 4 





8 



o o O o 



o o 

 o 



6 CD 



o 





5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 mm 



FIG. i. Relation between the lengths of males and associated females in 62 

 pairs of Gaminanis locusta; measurements in nims., for each pair; ordinates, 

 lengths of females ; abscissas, lengths of males. 



