176 MR. LUBBOCK ON SOME OCEANIC ENTOMOSTRACA 



perhaps, therefore, immature. Some of them had fom- joints, instead of three, to the 

 ahdomen : this is generally characteristic of the male sex ; yet these specimens agreed 

 with the others in the form of the abdomen and in other respects, and only differed from 

 the mature females in the form of the fifth pair of legs. We do not, however, yet know 

 whether, as in some other animals, the characteristics of the male sex appear first when 

 the animal is mature, or whether in the young male the abdomen, antennee, and fifth 

 pair of legs already resemble those of full-grown specimens. I am inclined to doubt 

 whether it be advisable to retain Dana's genus Hemiccdanus. The characters by which 

 it is separated from Diaptonius are not, I think, of great importance, and are both some- 

 w^hat inconvenient — the diiference of size in the fifth pair of legs in the female, from 

 being applicable only to one sex, and the absence of the four small intermediate segments 

 of the second pair of antennse, because the joints between these segments become fainter 

 and fainter so gradually that in some cases it is difficult to say whether they are present 

 or not. 



Mr. Darwin, in his admirable work 'On the Origin of Species' (p. 156), observes that 

 secondary sexual characters are very variable, that " species of the same group differ from 

 each other more widely in their secondary sexual characters than in other parts of their 

 organization ;" and again, " that the secondary sexual differences between the two sexes 

 of the same species are generally displayed in the very same parts of the organization in 

 wliich the different species of the same genus differ from each other." The Entomostraca, 

 and especially the Cyclopoidea, present remarkable examples of this law. In Fontella, 

 for instance, the sexual characters are afforded mainly by the anterior antennse and the 

 fifth j)air of legs. The specific differences also are principally given by these organs ; and 

 many of the generic characters in the Cyclopoidea are taken from the same source. 



The genera Calanus, Fontella, Euchceta, and others are very similar in form, live 

 together in the open sea, and probably upon nearly the same food, and might, at first 

 sight, be supposed to have similar habits. A glance, however, at the great differences in 

 many of their appendages shows that this cannot be the case, and proves to us how little 

 we really understand of their habits and mode of life. 



CALANID^E. 



Calantjs. 



1. Set<s antemiarum anticarum apicales subapicalibus loiigiores. Styli caudales vix 



oblongi. 

 Calanus laths, Lbk. 



Collected May 3, in S. lat. 0° 40', W. long. 0° 20'. 



2. Set(S antennaruni anticarum apicales suhapicalibiis breviores. 



A. Setce caudales mediocres. 



* Cephalothorax 5-6-artictdatus, piostice obtusiis aut breviter subacutus. 



Calanus setuligerus, Dana. 



My specimens differed from those described by Prof. Dana in having the cephalothorax 



