268 E. A. ANDREWS. 



On the whole the sex organs of Cambaroidcs are more like 

 those of Cambams than like those of Astaais. That is, the 

 hooks are present in Cambarns and Cambaroides, but not in 

 Astacus. From their form we may infer that in Cambaroides they 

 are used to hold the female just as they are used in Cambams. 

 The stylets in Cambaroidcs lack the flat scroll form of Astacus 

 and are more like the stout complexly tipped organs of Camba- 

 ms, but they are much more simple. They doubtless serve to 

 transfer the sperm as in both Astacus and Cambams. In the 

 female the annular plate of Cambaroides lacks the special sperm 

 reservoir of Cambams and is thus like Astaais, but it is more 

 developed and somewhat hollowed out. In this respect it recalls 

 the earliest phase of the ontogeny of the annulus of Cambams. 1 

 In brief the organs of Cambaroides are more simple than those 

 of Cambams but fashioned somewhat like them, suggesting some 

 connection closer with Cambams than with Astacus. 



How are these facts to be interpreted? The general anatomy 

 shows that Cambams is the recent and Astacus the more unspe- 

 cialized genus. Is Cambaroides a step from Astacus toward Cam- 

 bams or is it a step backward from Cambams ? 



Since Cambaroides has the same gill formula as Astacus and is 

 like Astacus in having no sperm receptacle (as far as known), 

 while on the other hand it has hooks like Cambams and stylets 

 similar to those of Cambams, we may regard it as a genus sep- 

 arate from both Astacus and Cambams. 



It then becomes a question of the relative positions of these 

 three genera. Granting that the larger number of gills is primi- 

 tive and the small number derived we must assume either that 

 the presence of hooks in Cambams with few gills and in Cam- 

 baroides with more gills is a case of secondary convergence from 

 parallel variation or else that it is a common inheritance. Ort- 

 mann has assumed the resemblances of Cambams and Cam- 

 baroides due to convergence, but Faxon regarded them of more 

 significance. The new facts as to the annular plate and the struc- 

 ture of the stylets will aid in the solution of this question ; with 

 emphasis upon the sex organs as criteria of relationship, which 

 has been the tendency of all recent work upon this group. 

 BIOL. BULL., X., Figs. 6, 7. 



