REPRODUCTIVE ELEMENTS IN APUS AND BRANCEIPUS. 277 



in a single instance. This renders the chances of proper fer- 

 tilisation very rare^ and, as all the specimens are equally pro- 

 lific, we must look either to hermaphroditism or partheno- 

 genesis as the means by which the embryonic development 

 is started. The hermaphrodite character has recently been 

 ascribed to the genital gland of various species of Apus, and 

 certainly the appearances which have come under my notice 

 favour this view.^ It is, however, immaterial to the line of in- 

 quiry I have adopted, which method of reproduction actually 

 obtains. The genital gland is an irregular tube with numerous 

 diverticula branching out on all sides. The cells lining the 

 main tube and its numerous ramifications are excessively 

 minute columnar bodies (figs. 24, 31, and 35 — 37), and the whole 

 appearance is far more like that of an Invertebrate intestine 

 than a reproductive gland. Each of the epithelioid cells con- 

 taios a small peculiar nucleus (fig. 36), whose position in the 

 rod-shaped mass of protoplasm it dominates, varies in concert 

 with all the nuclei of the same diverticulum. The nuclei oscil- 

 late backwards and forwards from the extremities of the cells 

 nearest the lumen of the gland to those nearest the basal 

 membrane bounding at its periphery. When in the former 

 position, such protoplasm as remains between them and the 

 actual glandular cavity is seen to be rapidly degenerating into 

 masses of slime (fig. 31) ; and, just as in the case of Branohipus, 

 this slime is ultimately worked up into an ornamental egg- 

 case. When the nuclei have translocated themselves towards 

 the bases of the cells, the slime has broken away in streaks 

 and globules, and many nuclei are seen subdividing themselves 

 into groups, from whose derivatives the nuclei of the future 

 eggs are formed (figs. 25, 27 — 29, 31). 



It is thus obvious, that for some reason or other an economy 

 has been effected in the reproductive apparatus of Apus, and 

 that there is no such permanent difi'erentiation between slime 

 and egg-producing cells as is apparent in Branchipus, but that 



^ For an account of this see the description of Siebold's results in the 

 'Klassen und Ordnungen des Thier Reichs,' pp. 960—962. Also H. M. 

 Barnard's ' Apodidae,' 



