LACINULARIA SOCIALIS I 39 



It will be observed that all these authors consider the winter ova 

 or ephippial ova and the ordinary ova to be essentially identical, only 

 that the former have an outer case. The truth is, that they are 

 essentially different structures. The true ova are single cells which 

 have undergone a special development. The ephippial ova are 

 aggregations of cells (in fact, larger or smaller portions — sometimes 

 the whole — of the ovary), which become enveloped in a shell and 

 simulate true ova. 



In a fully grown Lacinularia which has produced ova, the ovary, 

 or a large portiom of it, begins to assume a blackish tint (fig. 20) ; the 

 cells with their nuclei undergo no change, but a deposit of strongly 

 refracting elementary granules takes place in the pale connecting 

 substance. Every transition may be traced from deep black portions 

 to unalt^ed spots of the ovarium, and pressure always renders the 

 cells with their nuclei visible among the granules. The investing 

 membrane of the ovary becomes separated from the dark mass so as 

 to leave a space, and the outer surface of the mass invests itself with a 

 thick reddish membrane (fig. 21), which is tough, elastic, and reticu- 

 lated from the presence of many minute apertures. This membrane 

 is soluble in both hot nitric acid and caustic potass.'^ 



The nuclei and cells, or rather the clear spaces indicating them, 

 are still visible upon pressure, and may be readily seen by bursting the 

 outer coat. 



By degrees the ephippial ovum becomes lighter, until at last its 

 colour is reddish brown, like that of the ordinary ova ; but its contents 

 are now seen to be divided into two masses — hemispherical from 

 mutual contact (fig. 22). If this body be now crushed, it will be 

 found that an inner structureless membrane exists within the fenes- 

 trated membrane, and sends a partition inwards, at the line of 

 demarcation of the two masses (fig. 23). The contents are precisely 

 the same as before, viz., nuclei and elementary granules (fig. 24). 

 This, indeed, may be seen through the shell without crushing the 

 case. 



I was unable to trace the development of these ephippial ova any 

 further. Those of Notomniata, it appears, lasted for some months 

 without change (Dalrymple). 



It is remarkable that in Lacinularia these bodies eventually, like 

 the ephippium ol Daphnia, contain two ovum-like masses; and there 



^ Leydig [ioc. cit. p. 453) says that the shells of the ova were not dissolved by maceration 

 in a. solution of caustic soda (cold ?) for twenty-four hours, and thence concludes that they 

 may be composed of chitin. 



The above observation tends to the contrary conclusion. 



