ECONOMY OF THE DAPHNIA. 165 



or slightly oval, except where mutual pressure distorts them ; I 

 believe this to be only another form of the white deposit of 

 D. SchcE^eri. 



I was fortunate enough to witness on one or two occasions the 

 moulting of these creatures. The cuticle splits in definite 

 directions, one across the region of the heart, and another extend- 

 ing from the base of the great antennae to the posterior margin of 

 the valves (see//, Fig. 2). In DapJmia rotimda I have observed 

 that the line of fission passes between the reticulations of the 

 valves, but never across them (see Fig. 25), and the fact that the 

 reticulations in this part of the shell are so arranged as to leave 

 straight lines between them in the line of fission, shows that the 

 splitting of the cuticle is a matter not by any means of accident, 

 but of careful prevision. In DapJviia psittacea, the line of fission 

 is indicated by a row of minute spines. After the split had taken 

 place across the heart, the head and antennae were withdrawn, then 

 the lateral split along the line of spines took place, and the valves 

 being loosened, came off. The anal hooks and the covering of 

 the feet were the last to come away ; but these were thrown off 

 slowly, and impeded the respiratory movements for some time. 

 The exactness with which every detail of the process of moulting 

 is carried out is well illustrated by the account of the mode in 

 which the ephippium is cast, which has been furnished by Mr., now 

 Sir John Lubbock, in the Philosophical Transactions of the 

 Royal Society for 1857, part I., vol. 147 ; but to understand this, 

 it is necessary again to bear in mind that the wall of the carapace 

 is double, and that the new carapace is formed from the living 

 epidermis within the cavity — i.e., between the double wall of the 

 old carapace, and that the ephippial eggs are lodged in a specialized 

 portion of the brood receptacle between th,e valves. 



The ephippium, as it is found after the moult (Figs. 2, 24, and 

 28), consists of an external bivalve case, enclosing another ; 

 within which last are found the eggs. The external case is formed 

 from a portion of the outer wall of the old shell of the Daphnia, 

 and the inner case from a corresponding portion of the inner wall, 

 and the newly-formed shell is drawn out from between the two, 

 without disturbing the relative positions of the differentiated 

 portions, which make the outer and inner cases of the ephippium; 

 so that after the moult the two cases are found one within the 

 other, as they were before, although the new shell of the parent 

 has been drawn out from between them. The ephippium thus 

 cast off with the old cuticle, speedily becomes detached therefrom, 

 the connection between them at the time of moulting being very 

 fragile; in fact, only just sufficient to enable them to come 

 away together. 



