10 



M. H. S., Photo. 

 Plate III. — First and second pairs of swimmerets, of the male and female, 

 showing the changes which have taken place in the male. (Those of the 

 male on the left, the female on the right.) 



membranes, which are fused along the median line uniting the 

 pair of appendages. In the natural position this membrane 

 forms a crude tube with a slightly enlarged apex. The second 

 pair are less modified, the only change being a short spine devel- 

 oped on the inner side of the inner filament. During copulation 

 the tube of the first pair functions in the transference of the 

 sperm, while the second pair aid as supporting organs in some 



