- 



CRUSTACEA BRAXCHIOPODA 



CHAP. 



parent is not used as a protection for the winter-eggs., although 

 it is irenerallv. if not invariably, thrown off when the eir^s are 



-. i 



laid. In the Lynceidae the cuticle is moulted in such a way 

 that the winter-egirs remain within it. at least for a time ; the 

 cuticle is occasionally modified before it is thrown off: thus in 







<i.rns the cuticle of the carapace, in the 



. _:on of the broo i - pouch, becomes thickened and darkly 



coloured, forming a fairly strong case round the __-. The 



modification of the cuticle round the brood-pouch is much more 



-.lounced in the Daphniidae, where it leads to the formation of 



a lie-shaped cuticular box. the " ephippium," in which the 



\vintei---__- tre enclosed. The ripening of a winter-egg in the 



ovary of a Daphnia is accompanied by a great thickening of 



the eu:icle of the carapace <;r. Fig. IS . so that a strong case is 



formed in the position of 

 the brood-pouch. The 

 winter-egirs are laid be- 

 tween the two valv> - 

 this case, and shortly 

 afterwards the parent 

 moults. The eggs are 

 retained within the 



.ippium, from which the rest of the cuticle breaks away Tig. 

 A: - iration, the ephippium, which contains a single 

 ~irf'$tri.s or usually two 'Df.ipli.ni.fi. etc.,, either 

 sinks to the bottom, as in Mt or flo 



T..e winter- __- usually -_ r o through the earlv stages of 



V C7 



- .mentation within a short time after they are laid, but after 



_ T or shorter period of quiescence occurs, during 



which ' sjgs may be dried or frozen without injury. The 



ia md floor of a dried -up pond are often crowded with 



.ippia. containing winter-eggs which develop quickly when 



in water ; and the resting-stage of winter-eggs pro- 



in aquaria can often be materially shortened by drying 



which contain them, though such desiccation 



. :.- -- ary for development. Under 



normal conditions lar_re numbers of winter ->-__- remain 



qu: through the winter and hatch in the following 



1 - Newly-cast ephippium of 

 contai:. ing 1 





_ 



The individual developed from a sexually fertilised winter- 



