250 STALK-EYED CRUSTACEA. 



may well be that after these tj'pes had become acclimated to the depths, 

 their \'ouiig still found in the ancestral surface life the conditions most favor- 

 able for their development. The toad still goes to the water to spawn, the 

 land-crab goes to the sea. The journey of a swimming prawn from a depth 

 of 1000 fathoms or more to the surface to spawn does not impress one as 

 more remarkable than the periodic passage of anadromous fishes from the 

 sea to fresh waters in their solicitude for the welfare of their young. The 

 advantage gained for the race, too, through the wide dispersal of pelagic 

 larvie by the ocean currents is obvious. 



Most of the Stalk-eyed Crustacea, as is well known, protect their eggs 

 for a longer or shorter period after they are laid, either carrying them under 

 the tail, or, as in the Schizopoda, brooding them in a special pouch beneath 

 the breast. In many of the deep-sea species the eggs attain an enormous 

 size before they hatch. From analogy with certain land and fresh-water 

 species, we infer that in these cases the yoiuig quits the egg, or, which is the 

 same thing, leaves the mother in an advanced stage of development, ready 

 to lead a life similar to that of its parents. But it is a remarkable fact that 

 none of the deep-sea swimming forms belonging to the family Peneidae are 

 ever found carrying their eggs. The natural inference from this is that the 

 young must be quickly hatched, in a very immature state, best fitted for sur- 

 face life, like the larvie of the littoral species belonging to the same family. 

 This certainly adds weight to Spence Bate's suggestion concerning the occa- 

 sional occurrence of such forms at the surface. It is also worthy of note in 

 this connection, that Acanthephyra ngassizii, one of the Hoplophorida3 that 

 has been taken at the surface, has eggs of normal size. 



