NOTES ON THE DEVELOPMENT OF THE ARANEINA. 169 
bodies is, however, in the main destined to give rise to fresh 
cells which enter the blastoderm. 
I have not elucidated to my complete satisfaction the next 
stage or two in the development of the embryo ; and have 
not succeeded in completely reconciling the results of my 
own observations with those of Claparede and Balbiani. In 
order to show exactly where my difficulties lie it is necessary 
briefly to state the results arrived at by the above authors. 
According to Claparede the first difi“erentiation inPholcus 
consists in the accumulation of the cells over a small area to 
form a protuberance, which he calls the primitive cumulus. 
Owing to its smaller specific gravity the part of the ovum 
with the cumulus always turns upwards, like the blasto- 
dermic pole of a fowPs egg. 
After a short time the cumulus elongates itself on one 
side, and becomes connected by a streak with a white patch, 
which appears on the surface of the egg, about 90° from the 
cumulus. This patch gradually enlarges, and soon covers 
the whole surface of the ovum except the region where the 
cumulus is placed. It becomes the ventral plate or germinal 
streak of the embryo, its extremity adjoining the cumulus 
is the anal extremity, and its opposite extremity the cephalic 
one. The cumulus itself is placed in a depression on the 
dorsal surface of the ovum. Claparede compares the cumu- 
lus to the dorsal organ of many Crustacea. 
Balbiani (No. 1) describes the primitive cumulus in 
Tegenaria domestica, Epeira diadema, and Agelena labyrin- 
thicuy as originating as a protuberance at the centre of the 
ventral surface, surrounded by a specialised portion of the 
blastoderm (p. 57), which I will call the ventral plate. In 
Tegenaria domestica he finds that it encloses the so-called 
yolk-nucleus, p. 62. By an unequal growth of the ventral 
plate the primitive cumulus comes to be placed at the 
cephalic pole of the ventral plate. The cumulus now 
becomes less prominent, and in a few cases disappears. In 
the next stage the central part of the ventral plate becomes 
very prominent and forms the procephalic lobe, close to the 
anterior border of which is usually placed the primitive 
cumulus (p. 67). The space between the eumulus and the 
procephalic lobe grows larger, so that the latter gradually 
travels towards the dorsal surface and finally vanishes. 
Behind the procephalic lobe the first traces of the segments 
make their appearance, as three transverse bands, before a 
distinct anal lobe becomes apparent. 
The points ^^hich require to be cleared up are, (1) what 
is the nature of the primitive cumulus? (2) where is it 
