619 



exactly the advantages of a card catalogue, which are too well known to 

 require further comment. 



h. It must not be understood that these suggestions from degene- 

 ration are to be received as an absolute dictum from which there can be 

 no appeal. 



On the contrary, it may well be found that it is not feasible to use 

 as a basis of division just that thing which possesses the highest systematic 

 value. 



In such a case the testimony of degeneration should influence us 

 to select the highest basis available and should keep us from being 

 satisfied with the lowest. Giesbrecht tried the structure of the first 

 antennae as a basis for his second division and it did not prove satis- 

 factory. Just here can be found another strong recommendation of the 

 scheme proposed by Sars; it allows us to use a different basis in the 

 various sub-groups as often as the conditions warrant it. Sars' sub- 

 group Calanoida is the equivalent of Giesbrecht's Gymnoplea, but 

 while the latter author included all the rest of the copepods in the 

 Podoj^lea, or at least made the effort, and was thereby forced to divide 

 them all on a common basis, Sars divided the same families into six sub- 

 groups, and is thereby free to use six bases of division if necessary. 



He has already shown the wisdown of this: his division of the 

 Calanoida was made on the basis of the structure of the first antennae, 

 than which there could be nothing of higher systmatic value. But this 

 was not found to be as feasible in the Harpacticoida, and accordingly 

 he divided this second sub-group upon the structure of the mouth-parts, 

 the basis next in rank, and the third subdivision was based upon the 

 structure of the first swimming legs, again the basis next lower in value. 



From these considerations it would seem as if, after often repeated 

 changes and more than one hundred years of discussion, we have at last 

 a solid foundation, upon which in due time there is good hope of being 

 able to rear a permanent systematization of the copepods. 



By adopting these considerations, therefore, we have the order 

 Copepoda divided into seven suborders. 1) The Calanoida, free living and 

 pelagic. 2) The Harpacticoida, also free living but demersal. 3) The 

 Cyclopoida, partly free-living and freshwater species, partly commen- 

 sals and messmates with other animals, partly parasitic. 4) The N o te- 

 de Iphyoi da, semi-parasitic and living upon ascidians and similar 

 animals. 5) The Monstrilloida partly parasitic and partly free. 6) The 

 Caligoida, parasitic upon fishes, moderately degenerate and with some 

 freedom of motion. 7) The Lernaeoida, fish parasites, strongly 

 degenerate, fixed in position, and with marked sexual dimorphism. 



The sub-group Calanoida has been divided into three tribes upon 



