SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 94 



at the same time the size is increased, so that each ovisac contains 

 very few eggs, in some instances only two as shown in figure 7, an 

 harpactid, or a few more as in figure 8, a cyclopid. 



In addition to the modifications in structure exhibited by these sand 

 and mud dwellers, there are also such dififerences in habits and mode 

 of Hfe as would be expected from their habitat. Free-swimming cope- 

 pods maintain nearly perpetual motion ; as they are heavier than water, 



0.10 



Fig. 



7. — Dorsal view of female Goffinella stylifer, a sand dweller, 

 showing the peculiar ovisacs and large eggs. 



this is necessary to keep them suspended and prevent their sinking 

 to the bottom. When they wish to rest, some species are able to 

 suspend themselves from the surface film of the water, but all the 

 others must find some support. For those that live near the bottom, 

 the vegetation and the debris that collects on the bottom afiford the 

 requisite support, but it is quite different with those that live in the 

 open ocean. For them, unless there happens to be something floating 

 to which they can cling, it becomes the simple problem of sink or swim. 



