Hermaphroditism among the Apodidse. 301 



the production of these minute cells is a parallel phenomenon 

 with that accompanying the production of the eggs. This, it 

 seems to me, goes far to justify the assumption that these 

 cells are the male reproductive elements. 



In contrast to this minute pocket, in another section I have 

 noticed one or two very large irregularly shaped sacs in 

 which the epithelium was divided up into sperm-cells ; one 

 occurs, for instance, at the extreme anterior end of the gland 

 dorsally. 



I stated in my letter to * Nature,' above cited, that these 

 sperm-cells could be seen lurking in the folds of the genital 

 duct, apparently for the purpose of fertilizing the eggs in iheir 

 downward passage into the egg-pouch. The duct in the 

 longitudinal sections of the Spitzbergen Lepidurus is con- 

 tracted and is filled with a solid strand of slime resting on 

 the round ends of the club-like epithelium, which runs far 

 down the duct almost to its aperture. In the sections of Lepi- 

 durus productus the ducts must have been recently stretched. 

 The following structural details can be made out (PI. XI. 

 fig. 5 h). Externally is a thin layer of irregularly branching 

 or crossing muscle-fibres [mf) . Upon these rests the basement 

 membrane (Z*?«), which is finely wrinkled. Upon this membrane 

 small clear nuclei, each with a single chromosome and exactly 

 resembling the cells above described, occur irregularly, here 

 thickly, there very sparsely. Over the whole is an irregular 

 reticulum of slime with slime-granules. These clear cells are 

 evidently the cells which I referred to as the lurking sperm- 

 cells. Re-examination of them has not shown that they are 

 not; but beyond their close resemblance to the sperm-cells, 

 taken in conjunction with the fact that pockets of such cells 

 occur in the main genital tube quite close to the duct, there 

 is nothing to show for certain that they are. It is possible 

 that they may be the nuclei of the cells lining the duct, which, 

 in its contracted state, are long and club-like, but in its 

 stretched state must be flat and extended. They may be 

 perhaps a trifle larger than the sperm-cells, which range from 

 4 to 5 /i, these from 5 to Q fi. On the other hand, they occur 

 very irregularly, often in groups, whereas we should rather 

 expect the nuclei of the epithelial cells to be uniformly and 

 rather sparsely spread over the surface. 



Most of the unripe eggs in this specimen appear to be 

 degenerating. 



Apus cancrijbrmis. 



Of the three series of sections of this species, as above 

 stated, only one, and that the very first examined five years 



