80 HISTORY OF CRUSTACEA. CHAP. VIII. 



hand in the second pair of feet is uniformly con- 

 vex, the last pair of feet is slender and similar 

 to the preceding. Subsequently the antennae become 

 thickened, two, three, or four of the first joints of the 

 flagellum are fused together, the palm of the hand 

 acquires a 'deep emargination near its inferior angle, 

 and the intermediate joints of the last pair of feet 

 become swelled into a considerable incrassation. No 

 museum-zoologist would hesitate about fabricating two 

 distinct species, if the oldest and youngest sexually 

 mature males were sent to him without the uniting in- 

 termediate forms. In the younger males of Orchestia 

 Tucuratinga, although. the microscopic examination of 



Fig. 50. is Fig. 51 



their testes showed that they were already sexually 

 mature, the emargination of the clasping margin of the 

 hand (represented in fig. 50) and the corresponding pro- 

 cess of the finger, are still entirely wanting. The same 

 may be observed in Cerapus and Caprella, and probably 

 in all cases where hereditary sexual differences occur. 



15 Fig. 50. Foot of the second pair (" second pair of gnathopoda ") of 

 the male and fig. 51 of the female, of Orchestia Tucuratinga, magn. 15 

 diam. 



