NOTES ON THE EMBRYOLOGY OF L1MOLUS. 
523 
similar correlation between the vitality of the individual and 
of the race in the case of the Brachiopods. 
The eggs vary considerably in their characters. Some are 
spherical, others markedly oval. According to my measure- 
ments the average diameter is about two millimetres, varying 
between l - 75 mm. and 2 - 2 mm. Some are brown, some are 
ashy green, and others yellow or pink. Color seems unim- 
portant, as I have had pink embryos hatch, the color persisting 
for some time after escape from the membranes. The egg is 
enveloped in a thick and dense chorion, which is apparently 
made up of layers, about twenty in number, the whole having 
a total thickness of about yoVo^ an i QC h- In rupturing 
this chorion the line of tear usually goes straight across, and 
but rarely can traces of lamination be seen. Usually no traces 
of pores are visible, and I have sought in vain for a micropyle. 
Occasionally I have seen indistinctly what may be pores, and 
it is certain, for reasons which will appear anon, that there is 
some way in which water penetrates the chorion. 
I greatly regret that I have nothing to offer regarding seg- 
mentation and the formation of the blastoderm, but my earliest 
embryos are already far along in their development. In the 
following pages I shall speak but briefly of the external de- 
velopment, except when my observations are at variance with 
the previously published accounts of Dohrn ('71) and Packard 
( J 72). In studying the internal development I am unfortunate 
in having no predecessor, as I thus have nothing with which to 
check my results, and hence there is more chance for error to 
creep in. Even more unfortunate is the fact that I have no 
knowledge of the formation of the blastoderm wherewith to 
settle some features of the later stages which are uncertain. 
External Development. 
The earliest egg seen was treated with osmic acid, and pre- 
sented the appearance shown in fig. 4. Upon the surface is a 
longitudinal pyriform depression in the centre of a lighter field. 
This lighter area corresponds to the germinal area so frequently 
