APPENDIX IV 307 



tion of the ectoderm. As a starting point for such a com- 

 parative study we should like here to emphasise the fact 

 that, if our theory is correct, the primitive structure of the 

 organ is most probably to be found in the larva of Apus, 

 and that its form in the other Crustacea must have been 

 derived from that. We do not therefore see any reason 

 to modify our suggestion as to its origin because of the 

 fact that in the higher Crustacea it first appears as a more 

 complicated, and even sometimes as a paired, organ. 



It is this organ which, in the Daphnidae, functions as a 

 sucker for fixing the little animals to stationary objects. The 

 glandular nature of the organ might easily be supposed to 

 assist this action by supplying a slimy secretion. 



X 2 



