250 THE AX ATOMY OF IXVERTEBRATED ANIMALS. 



of the genus Daphnia will thus go on producing broods for 

 generation after generation, without any known limit. 1 



Under certain circumstances, however, bodies of a differ- 

 ent nature from these " agamic ova," as they have been well 

 termed by Sir John Lubbock, 1 are developed within the 

 ovary, the substance of which acquires an accumulation of 

 strongly refracting granules at one spot, and forms a dark 

 mass, the so-called " ephippial ovum." When fully formed, 

 two of these bodies pass into the dorsal chamber of the cara- 

 pace, the w 7 alls of which have, in the mean time, become 

 altered. The outer and inner layers of the integument ac- 

 quire a peculiar structure, a brown color, and a more firm 

 consistency, over a large, saddle-like area. When the next 

 moult takes place, these altered portions of the integument, 

 constituting the "ephippium," are cast off, together with the 

 rest of the carapace, which soon disappears, and then the 

 ephippium is left, as a sort of double-walled spring-box (the 

 spring being formed by the original dorsal junction of the 

 two halves of the carapace), in which the ephippial ova are 

 inclosed. The ephippium sinks to the bottom, and, sooner 

 or later, its contents give rise to young Dajyhnioe. 



Jurine's and Sir J. Lubbock's researches have proved that 

 the development of the ephippial ova may commence with- 

 out the influence of the male, and they seem to indicate that 

 these ova may even be fully formed and laid without the 

 male influence. On the other hand, there appears, under ordi- 

 nary circumstances, to be a certain relation between the com- 

 plete development of ephippial ova and the presence of males ; 

 and, as yet, no ephippial ova produced by virgin females have 

 been directly observed to produce young. The question, 

 therefore, seems to stand thus, at present: the agamic ova 

 may certainly be produced, and give rise to embryos, without 

 impregnation ; the ephippial ova may certainly be produced 

 without impregnation ; but whether impregnation is or is not 

 absolutely necessary for their further development, there is, 

 at present, no evidence to show. 



The great majority of the JBranchiopoda inhabit fresh 

 waters. Artemia, however, delights in brine-pools. The 

 genus Estheria is of Devonian age, and it seems probable 



lU Ueber die Gattungen Estheria und Limnadia." (" Archiv fur Natur- 

 geschichte," 1854.) 



2 " An Account of the Two Methods of Reproduction in Daphnia, and of the 

 Structure of the Ephippium." (" Transactions of the Royal Society," 1875.) 



