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. 



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 oi Pteronarcys with 

 those o^ 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 that 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. lAx) 

 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 csecal 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 its 

 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 dilated 

 oviduct, which commences in the egg-chamber, in the female, and which 

 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 



