NO. 7 A NEW COPEPOD HABITAT WILSON I3 



the bursting of the first and the last egg shell. Here also the female 

 copepod is moving about constantly while the nauplii are emerging, 

 so that the latter are just as widely separated as when the eggs were 

 deposited singly. Such a scattering of the larvae must contribute 

 greatly to a wide distribution of the species, but we are chiefly con- 

 cerned here with the separation of parent and ofifspring. It is quite 

 evident that among these free-swimmers no inference of relation- 

 ship can be drawn from a mere association of adults and larvae. 



In the commensal copepods, on the contrary, every step in the 

 process of reproduction from the preliminary mating to the final 

 moult into the adult form takes place within the body of the host. 

 If there were a single male and female at the outset it would be fairly 

 certain that all the larvae were their ofifspring, and we would have a 

 genuine copepod family from a genetical point of view. Relationship 

 can be argued here from association of adults and larvae and might 

 possibly continue through more than one generation. 



The terraqueous copepods appear to occupy an intermediate posi- 

 tion between the two extremes just noted. Compared with the free- 

 swimmers the)^ move about very little, compared with the commensals 

 they have greater freedom of locomotion. It is highly probable, how- 

 ever, that the area covered by a female during the hatching of her 

 eggs is very limited. As a result the emerging nauplii are not far 

 removed from their parent and may be more or less closely associated 

 with one another. The relationship of adults and larvae found together 

 is not at all impossible, but neither is it as probable as among the 

 commensal copepods. 



The considerations here discussed show very clearly that these 

 terraqueous copepods constitute a fourth group fully as well defined 

 as either of the three already accepted. And they open up to the 

 investigator an entirely new field of research along several interesting 

 lines. Not only will a comparatively large number of the specimens 

 obtained in the sand and mud prove to be new species and genera, 

 but also they will exhibit some remarkable adaptations to their en- 

 vironment. The habitat is entirely new and one of the last to be 

 suspected as a resort for copepods, and the mode of life is unicpe and 

 entirely unlike that of other copepods. Such a combination ought 

 to prove genuinely attractive and, supplemented by the abundant sup- 

 ply of working material, ought to yield important results. 



