Affinities of Pteronarcys regalis. 445 
of this species, of which I have dissected several, have not the slightest 
rudiment of process from the eighth segment, nor any enlargement of its 
margin. l 
These marked differences of structure in the external organs of repro- 
duction still further distinguish Perla and Pteronarcys, and seem to indi- 
cate that there are some differences of habit on the part of the females with 
regard to their oviposition. Of the internal anatomy of the female I can 
only speak generally, as I have not been able to procure a specimen suffi- 
ciently good for precise description. The only one I have dissected had 
originally been preserved in a dried state. It may, nevertheless, be of use 
to compare the few facts I have noticed in the anatomy of Pteronarcys with 
those of Perla, more especially as the internal reproductive organs have not 
yet been described in the former of these genera. The general structure in both 
is similar, and tbat of the organs in the two sexes differs less than in most other 
insects. In Perla as in Pteronarcys the follicular testis of the male (fig. 14 x) 
is represented by a multitude of short ovigerous tubes, which, aggregated 
together around and opening into a common duct or cavity, constitute the 
ovary in the female. Each egg-tube, of which there are upwards of twenty 
in each ovary, is filled with at least ten distinct rudimentary ova, which give 
it a beaded or nodulated appearance. It is large and dilated at its base, 
and is rapidly diminished in size in proportion to the distance of its attach- 
ment around the egg-chamber of the duct. It is the representative of the 
Short ezecal follicle (fig. 15) in which the spermatozoal cells are formed in 
the male, and which, instead of being arrested at the follicular stage of 
development, continues to be elongated, while some of the nuclei of ite 
centripetal layers of cells, in which the forces of growth are most energetic, 
become individualized as separate organisms, the germs of future ova, and 
Which, more rapidly nourished by the principle of endosmose than the sur- 
rounding cells, constitute the materials of future beings. In like manner the 
convoluted spermatic duct of the male (x, y) is represented by a long m 
oviduct, which commences in the egg-chamber, in the female, = whieh 
«differs but little, except in diameter, from the spermatic or deferential duct 
of the male; and, like it, terminates, by junction with its fellow of the oppo- 
site side, in a common passage for the eggs, the analogue of the ejaculatory 
