Phylctic Parallelism in Mctamorphic Species. 5 1 7 



but the antennae of the males differ to a remark- 

 able extent, as was first correctly shown by 

 Leydig. 



Similarly in the case of genera there may be 

 observed an incongruence of such a kind that in- 

 dividual parts of the body may deviate to a 

 greater or to a less extent than the corresponding 

 parts in an allied genus. If, for instance, we com- 

 pareaspecies of thegenusof Daphniacea,&V&,with 

 a species of the nearly allied genus Daphnella, we 

 find that all the external and internal organs are in 

 some measure dissimilar nevertheless certain of 

 these parts deviate to an especially large extent, 

 and have without question become far more trans- 

 formed than the others. This is the case, for 

 example, with the antennae and the male sexual 

 organs. The latter, in Daphnella, open out at the 

 sides of the posterior part of the body as long, 

 boot-shaped generative organs, and in Sida as 

 small papillae on the ventral side of this region of 

 the body. If again we compare Dapknella with 

 the nearly allied genus Latona, it will be found that 

 no part in the one is exactly similar to the 

 corresponding part in the other genus, whilst cer- 

 tain organs differ more widely than others. This 

 is the case for instance with the oar-like appen- 

 dages which in Latona are triramous, but in 

 Daphnella, as in almost all the other Daphniacea, 

 only biramous. 



In families the estimation of the form-divergence. 



