The First Abdominal Segment of Embryo Insects. 
127 
crowned with a few feeble hairs. The portion included between the lateral 
rims is flat and of a much paler color than the remainder of the integument, 
which is provided with an abundance of blue pigment. A very distinct 
slit divides^the organ into two symmetrical halves. This is all that can be 
seen from the surface; for further details recourse must be had to cross 
sections. (Fig. 15.) Here it is seen that the projection of the organ above 
the general surface of the segment is about equal to its diameter. The 
cuticle (ct.) is rather thick and externally very finely papillose. This un¬ 
evenness of surface is continued over the lateral rims, but where the 
center is depressed and paler the papillose cuticle is replaced by a smooth 
and more delicate layer (ct.), which stains pink in lithium carmine. This 
portion of the cuticle, deeply induplicated at the median slit that divides 
the organ into two symmetrical halves, evidently differs considerably in 
its chemical structure from the unstainable papillose cuticle covering the 
remainder of the body. The hypodermis forming the sides of the collo- 
phore has very large flattened nuclei ( hy .), which are almost concealed in 
the dense layer of pigment. Beneath it lies a mass of connective tissue 
(cn). At the inner boundary of the rim of the ventral face of the organ, 
where the papillose cuticle is replaced by the delicate and stainable layer, 
the hypodermis also undergoes a marked change. From being a rather 
thin, deeply pigmented layer with huge flattened nuclei it becomes a 
thicker layer of evenly granular, unpigmented protoplasm, smooth on its 
external face but raised into numerous rounded protuberances on its inner 
surface, (gl.) A spherical nucleus considerably smaller than those of the 
pigmented hypodermis, is lodged in each of these protuberances, which 
thus represent the different cells. These are not, however, separated by 
perceptible boundary lines; hence this modified portion of the hypodermis, 
and perhaps also the unmodified portion, is to be regarded as a syncytium. 
The whole of the hypodermis underlying the modified cuticle is peculiarly 
and symmetrically folded. In its center it presents a broad induplication 
corresponding with the narrower one of the superjacent cuticle. The cells 
forming this median portion are small and flat. On either side there is 
another rather deep infolding, to the inner angle of which a delicate muscle 
is attached, (ms.) The ventral nerve chain, indicated at n, runs beneath 
the median induplication. As may be seen from the figure, there is a wide 
space between the modified hypodermis and its cuticle. I have seen no 
traces of blood in this cavity, which in some specimens contains small 
masses of a granular and very deeply stainable secretion, (s.) Larger 
masses of the same substance are frequently seen clinging to the outer 
surface of the modified cuticle. I regard the modified hypodermis as the 
gland that secretes this granular substance. The cavity of the organ 
bounded on the outside by the hypodermis is filled with blood ( bl .) which, 
when the organ is called into action, is probably forced against the glandu¬ 
lar hypodermis, the two retractor muscles relaxing. Probably the infold¬ 
ing of the cuticle is pushed out simultaneously with the three infoldings 
