526 
J. S. KINGSLEY. 
the blastopore had closed in the middle, leaving the mouth 
and anus at the ends. This, I believe, is the true explana- 
tion, allowances being made for the modified form of gastru- 
lation ( vide infra). The fact that the narrow extremity of 
the oral opening is turned forwards is due to its being in the 
act of transference from a position in front of the first pair of 
appendages to one behind it. Between the mouth and anus 
is apparently a shallow groove. In reality this is produced by 
the neurulation, and is internal. Sections show that the 
external surface is smooth (fig. 47), and that the blastopore 
has entirely disappeared, except as mouth and anus. 
The first pair of abdominal appendages (opercula) are par- 
tially marked out, and it is to be noticed that these and the 
gill-bearing appendages develop in a slightly different manner 
from the true limbs, a fact which would not be inferred from 
Dr. Packard’s drawings (e. g. ’ 72 , ph iv, fig. 16). In reality 
they arise as broad plates, separated from the surrounding 
surface by a tucking in of the epiblast behind (cf. ‘ Forma- 
tion of Lungs of Scorpion/ Metschnikoff, ’ 71 , p. 225, pi. xvi, 
fig. 12). Besides the opercula the abdomen as yet shows no 
trace of segmentation or appendages. The limit of the meso- 
blast is much more distinct than in the preceding stage. It 
extends slightly beyond the limbs, and has an elongate oval 
outline slightly narrower in front. Outside the limits of the 
mesoblast, on a line between the fourth and fifch pairs of 
appendages, are seen the rudiments of the compound eyes. 
They are not visible in the living egg, but stain readily and 
deeply with osmic acid. 
Between this and the stage figured in 6 the changes are 
slight. This is slightly earlier than Dr. Packard’s (’72) pi. iv, 
fig. 16. The mouth and anus still retain the same outlines 
as before, and the neural groove is still conspicuous. The 
limbs are now elevated above the surrounding surface and 
begin to show traces of flexure. In the abdominal region the 
opercula are better developed and the first pair of gill-bearing 
appendages have appeared. In this and earlier stages I have 
failed to find that segmentation outside the mesoblastic area 
