The First Abdominal Segment of Embryo Insects. 105 
It is probable that they soon disappear without ever becoming bulbous, 
since a tendency thus to differentiate is distinctly manifest in other Orthop- 
teran embryos that have reached the age of the Mantis embryos figured by 
Graber. 
Neophylax concinnus. 
An isolated observation on pleuropodia in the Phryganeidae is embodied in 
one of Patten’s figures of a Neophylax embryo [’84, plate 36 A, Fig 11.] 
Patten notes the fact in the text [page 578] that three pairs of abdominal 
appendages are developed cn the basal segments, but says nothing about a 
differentiation of the most anterior pair. The figure referred to, however, 
shows that the conical abdominal appendages of the first abdominal seg¬ 
ment are considerably larger than those of the two succeeding segments. 
Dr. Patten has, at my request, kindly taken the trouble to re-examine his 
sections, and informs me that the cells of the pleuropodia differ in struct¬ 
ure from the unmodified ectoderm cells of the other appendages and the 
body wall of the embryo. 
Acilius. 
At my request, Dr. Patten has very kindly sent me the following de¬ 
scription of the pleuropodia of this Dytiscid: 
As in other forms so in Acilius , the pleuropodia arise on the first abdom¬ 
inal segment of the young embryo, as a pair of ectodermic evaginations, 
homostichous with the thoracic legs. Later, the distal end of each bul¬ 
bous appendage, consisting of large columnar cells, is invaginated in the 
form of a cup. The nuclei are situated in the inner ends of the cells, each 
of which secretes at its tip a short refractive thread, which, with those of 
the neighboring cells goes to form over the invaginated area a thick, 
striated, cuticula-like layer. Dr. Patten remarks that this form of secre¬ 
tion may be compared with the pleuropodial secretion of Zaitha, the only 
difference being that the individual threads secreted are so short as to form 
together a continuous sheet, instead of a penicillate bundle. 
These peculiar appendages, which of all described species most closely 
resemble the pleuropodia of Meloe, do not fall off during their period of 
degeneration, but are pushed into the yolk and absorbed. 
Hydrophilus piceus, L. 
The pleuropodia of this form were first observed by Kowalevsky [71.] 
They are distinctly seen in his Fig. 12, as digitiform processes, shorter than 
the metathoracic legs. Nothing is said of their differentiation. In the 
figure of an older embryo they are represented as a pair of smaller protuber¬ 
ances inserted on the pleurae near the bases of the metathoracic legs. 
Heider [’89] in the first part of his beautiful monograph, figures the 
pleuropodia of Hydrophilus in several places, [Figs. 2 and 3 in the text; 
