NOTES ON THE DEVELOPMENT OF THE ARANEINA. 177 
ga 7 iglionic thickening for the chelicerm quite independent of 
the procephalic lobes. 
In the procephalic lobes the epiblast is much thickened 
and is formed of several rows of cells. The greater part o^ 
it is destined to give rise to the supra-oesophageal ganglia. 
During the various changes which have been described the 
blastoderm cells have been continually dividing^ and, together 
with their nuclei, have become considerably smaller than at 
first. The yolk cells have in the meantime remained much 
as before, and are, therefore, considerably larger than the 
nuclei of the blastoderm cells. They are more numerous 
than in the earlier stages, but are still surrounded by a 
protoplasmic body, which is continued into a protoplasmic 
reticulum. The yolk is still divided up into polygonal seg- 
ments, but from sections it would appear that the nuclei are 
more numerous than the segments, though I have failed to 
arrive at quite definite conclusions on this point. 
As development proceeds the appendages grow longer and 
gradually bend inwards. They become very soon divided by 
a series of ring-like constrictions which constitute the first 
indications of the future joints (PI. XIX, fig. 6). The full 
number of joints are not at once reached, but in the ambu- 
latory appendages five only appear at first to be formed. 
There are four joints in the pedipalpi, while the cheliceree do 
not exhibit any signs of becoming jointed till somewhat later. 
The primitive presence of only five joints in the ambulatory 
appendages is interesting, as this number is permanent in 
Insects and in Peripatus. 
The next stage figured forms the last of the third 
period (PI. XIX, fig. 7 .and 7 a). The ventral plate 
is still rolled round the egg (fig. 7), and the end of the tail 
and the procephalic lobes nearly meet dorsally, so that there 
is but a very slight development of the dorsal region. There 
are the same number of segments as before, and the chief 
differences in appearance between the present and the 
previous stage depend upon the fact (1) that the median 
ventral integument between the nerve ganglia has become 
wider, and at the same time thinner ; (2) that the limbs have 
become much more developed ; (3) that the stomodaeum is 
definitely established ; (4) that the procephalic lobes have 
undergone considerable development. 
Of these features, the three last require a fuller descrip- 
tion. The limbs of the two sides are directed towards each 
other, and nearly meet in the ventral line. The chelicerae 
are two-jointed, and terminate in what appear like rudi- 
mentary chelae, a fact which perhaps indicates that the 
