EMBRYOLOGY OF CI.ErSINE. 243 



poles of the amphiaster, still connected by a slender band of 

 iiucieoplasni, have ])assed from a biconvex into a meniscal 

 form, with their concavities facing each other. 



Fig, 7(3 (3 h. 30 min) represents a stage about fifteen minutes 

 in advance of fig. 75, although, according to date, it should 

 be 30 minutes in advance. 



The first cleavage is seen at the moment of completion. 

 The larger of the two cleavage segments contains nearly all 

 of what is still visible of the two rings. The poles of the 

 amphiaster, between which only an attenuated thread of nuclear 

 substance is still seen, have returned from the meniscal to the 

 biconvex form, and are much nearer to each other than during 

 the process of cleavage. In each of these poles, which now 

 form independent centres, or nuclei, is a cluster of small bodies, 

 which have the microcheraical aspect of the three pronucleoli 

 before described, and which I therefore regard as nucleoli. 



The nucleoplasm of each nucleus is indistinctly divided into 

 two areas. The central area is not quite so highly coloured as 

 the peripheral, and corres))onds in general ajjpearance to the 

 stripe-areas seen in figs. 74 and 75. I think these stripe-areas 

 correspond to the clear central spaces seen in fig. 73, which become 

 flattened shortly before the cleavage. The rays, which reach their 

 greatest intensity in stage 74, have nearly or wholly disappeared 



Fig. 76 reminds one strongly of corresponding stages described 

 by Gotte (Bombiuator igneus) and Hertwig (Rana teinporaria). 



The five to six clustered nucleoli evidently correspond to 

 Hertwig's nuclei and to Gotte's " Kernkeime ^' (^). 



The clear central spaces (ca) that arise in the poles of the 

 amphiaster (fig. 73) probably correspond to Gotte's "Lebens- 

 keim-Cii). 



Summary. 



1. The germinal vesicle of the ovarian egg gives rise to a 

 bi-stellate figure (archiamphiaster), which gradually approaches 

 the surface of the egg, where, at the time of deposit, one pole of 

 the same becomes visible as a white stellate figure. 



2. The egg may be retained two da\s, possibly four or five, 

 after the transformation of the germinal vesicle, during which time 

 the archiamphiaster apjiears to remain in a queiscent condition. 



3. Tlie white stellate figure marks the place where the mouth 

 later forms, and hence this pole may be designated as oral, and 

 the opposite as ahoral. The line passing through the centre of 

 the egg, and joining these two poles, is the axis of the egg, and 

 corresponds to the longitudin.d axis of the future embryo. 



4. The oral pole is specifically lighter than the aboral pole 

 (hence alw;iys uppermost), is the seat of the unipolar phenomena, 

 and takes the lead in all tlio bi-])olar phenomena. 



