258 SOME RECENT 



Key West, in Florida, differed constantly from 

 individuals of the same species from N. Carolina, 

 and these again from individuals living at the 

 Bahamas. In other instances the differences in 

 development appeared to be related to the conditions 

 of life. At the Bahamas a species of Alpheus was 

 observed dwelling in the chambers of sponges. 

 Two kinds of sponge were employed by the prawn, 

 one sponge being green, the other brown. The 

 prawns living in the green sponge produced con- 

 siderable numbers of small eggs ; while the indi- 

 viduals of the same species which dwelt in the 

 brown sponge gave rise to a few eggs of large size, 

 from which the young prawns were hatched at a 

 stage corresponding to that reached at the third 

 moult by the young developed from the smaller eggs 

 in the green sponge. 



Another very curious series of facts has been 

 made known to us by the careful researches of the 

 Russian embryologist, Salensky, on the early 

 development of certain Ascidians. The normal 

 course of development in a Metazoon, as is well 

 known, is that the fertilised egg segments, i.e., 

 divides into a number of nucleated cells from which, 

 by further division, and accompanying differentia- 

 tion, all the various parts and tissues of the embryo, 

 and finally of the adult animal, are produced. 

 Every individual cell of the adult, whether an 

 epithelial cell, a nerve cell, a muscle cell, or a bone 

 cell, owes its origin to direct descent from the 

 original egg-cell or ovum. The most striking fact 

 in the whole range of embryology is that all 



