GROUP d 



245 



Figures of the copulatory organs of the four species have been grouped together in Fig. 28 so 

 that they may easily be compared. Those of E. spinifera and E. longirostris are very similar indeed, 

 although there are constant and unmistakable differences (p. 230). There is not so close a similarity 

 between those of E. ha?iseni and E. spinifera, but they are of the same plan: the terminal processes 

 are alike, and although the ends of the pro.ximal processes are quite different in outline they are both 

 membranous expansions in an approximately vertical plane. At least it can be said that the copu- 

 latory organ of E. hanseni is not more similar to that of E. longirostris than to that of E. spinifera; 

 it is certainly nearer to E. spinifera than to E. triacantha. That of E. triacantha is more unlike the 

 other three than any other — it appears as dissimilar to those of E. longirostris and E. spinifera as to 

 that of E. hanseni. 



There is an increase in the size of the species as one passes from warm to colder water, as the 

 following table shows: 



The larval stages of E. hanseni are not known. In E. spinifera and E. longirostris the Calyptopis and 

 earliest Furcilia stages have the edges of the carapace denticulate, more completely so in the latter 

 than the former; they have the same sequence of Furcilia stages. E. triacantha has a different 

 sequence of Furcilia stages; the edge of the carapace is not denticulate in the Calyptopis or Furcilia. 



To sum up : Each of the four species of Group d occupies one of four successive zones 

 of water from north to south. I take this to be such strong evidence of their evolutionary 

 relationships that I attach much more weight to the few characters which appear to 

 confirm it than to those which do not, since I see among the latter none which suggests 

 another order of relationship. 



The most striking fact brought out in the comparison of the four species above is the 

 close resemblance between E. spinifera and E. longirostris, the middle two of the series. 



