746 



THE THEORY OF TRANSFORMATIONS [ch. 



curved orthogonal system in Fig. 2, we at once obtain a very fair 

 representation of an allied genus, belonging to a different family 

 of amphipods, namely Stegocephalus. As we proceed further from 

 our type our co-ordinates will require greater deformation, and 

 the resultant figure will usually be somewhat less accurate. In 

 Fig. 3 I show a network, to which, if we transfer our diagram of 



Fig 370. 1. Harpinia plumosa Kr. 2. Stegocephalus infiatus Kr. 



3. Hyperia galba. 



Harpinia or of Stegocephalus, we shall obtain a tolerable representa- 

 tion of the aberrant genus Hyperia, with its narrow abdomen^ 

 its reduced pleural lappets, its great eyes, and its inflated head. 



The hydroid zoophytes constitute a "polymorphic" group,, 

 within which a vast number of species have already been dis- 

 tinguished; and the labours of the systematic naturalist are 

 constantly adding to the number. The specific distinctions are 

 for the most part based, not upon characters directly presented 



