The First Abdominal Segment of Embryo Insects. 
125 
when fully developed, it is, of course, possible that they may have contained 
evaginations of the mesodermic somites during the first stages of their 
development. We have a case in point in the pleuropodia of insect em¬ 
bryos. In the younger stages, as I have shown in Blatta, each of the two 
mesodermic somites of the first abdominal segment sends a papillar 
process into an evaginating pleuropodium in exactly the same manner as 
the mesodermic somites of the thorax send processes into the legs. Subse¬ 
quently, when the pleuropodia have become distinctly differentiated, the 
mesodermic elements, which in the thoracic appendages persist and are 
converted into muscles, are pushed back into the body cavity. Using 
Haase's criterion and considering only the mature appendages, we should 
not be justified in regarding the pleuropodia as true appendages. 
The evidence in regard to the origin of the styliform append¬ 
ages, which Haase has failed to give us, is at least in part supplied by 
Oudemanns [’87.] The Dutch investigator observed that of the three 
pairs of styliform processes occurring on the 7th, 8th and 9th abdominal 
segments in both sexes of Thermopliila furnorum, only one pair, and that 
the hindmost, was to be found in the youngest specimens examined. Next 
in order of time appears the pair on the eighth and finally the pair on the 
seventh abdominal segment. This manner of making their appearance, as 
Oudemanns suggests, is strong evidence against their being true append¬ 
ages. It may also be noted in this connection that the styliform append¬ 
ages even in those forms that possess many pairs are longest on the pos¬ 
terior segments and gradually diminish in length anteriorily. This is 
contrary to what we expect in true appendages; for these in insect em¬ 
bryos usually decrease in distinctness and prominence in the opposite 
direction. 
In the Collembola a peculiar organ, called by Packard the collophore, 
occurs in the median ventral line of the first abdominal segment. This 
organ is thus described by Lubbock (’73, p. 68): 
“Underneath the anterior abdominal segment is the ventral tube, or 
sucker. In Podura, Lipura, and the allied genera, this organ is a simple 
tubercle, divided into two halves by a central slit; in other genera, as, for 
instance, in Orchesella and Tomocerus, the tubercle is enlarged, and be¬ 
comes a tube divided at the free end into two lobes. In the Smynthuridae 
and Papiriidae the organ receives a still further and very remarkable de¬ 
velopment; from the end of the tube the animal can project two long, del¬ 
icate tubes, provided at their extremity with numerous glands.” 
Lubbock makes the following remarks on the function of the collophore: 
“ No one, indeed, who has watched the habits of the Collembola, can 
doubt its function. If a Smynthurus is laid on its back — a position from 
which it has some difficulty in recovering its feet — and if, while it is in 
this attitude, a piece of glass is brought within its reach, the animal will 
endeavor to seize it with the feet, but at the same time it will project one 
or both of the ventral tentacles and apply it, or them, firmly to the glass, 
