3io APPENDIX V 



the sperm-cells lurk. The eggs are then fertilised as they 

 stretch this membrane in passing out into the egg pouch. 

 The whole richly-branched reproductive organ, with the eggs 

 developing at the tips of the branches, and with here and 

 there a testis, strongly reminds one of a monoecious plant, 

 self-contained, and able to dispense with pollen from 

 without. 



I reserve the drawings and the more detailed description 

 of the reproductive organs of the different species for a short 

 comparative study of the Apodidae which I hope soon to 

 have ready for the press. 1 By way of caution, however, I 

 should here add that small yellowish sacs filled with minute 

 cells occur here and there among the developing eggs. 

 These must not be mistaken for the testes. They are the 

 loci of discharged eggs, and the minute cells are the epithe- 

 lium cells dislodged by the shrinking of the membrane of 

 the genital tube, which is stretched some loo-fold by the 

 ripening eggs. 



The origin of this secondary hermaphroditism is not far 

 to seek ; it is clearly a protection against isolation, as in the 

 case of the Cirripedia and certain parasitic Isopoda. The 

 manner of life of all these animals is such that they are 

 always in danger of being cut off from their kind ; they would 

 thus die out unless able to reproduce either parthenogeneti- 

 cally or by means of self-fertilisation. 



Some species of Cirripedia, as is well known, have dwarf 

 males, the last remains of the original separation of the 

 sexes. As already mentioned, small males of Apus cancri- 

 formis are sometimes found. Twelve finds of A. cancriformis 

 and L. productus recorded by Gerstaecker, give 4,458 

 "females" (i.e. hermaphrodites) to 378 males; while sixteen 



1 As stated in the Preface, this intended work gave way before the 

 more ambitious task of trying to prove Apus to be but a modified 

 carnivorous Annelid. 



