XVII] THE COMPARISON OF RELATED FORMS 1055 



Diirer was acquainted with these oblique coordinates also, and I 

 have copied two illustrative figures from his book*. 



In Fig. 511 I have sketched the common Copepod Oiihona nana, 

 and have inscribed it in a rectangular net, with abscissae three-fifths 

 the length of the ordinates. Side by side (Fig. 512) is drawn a very 

 different Copepod, of the genus Sapphirina ; and about it is drawn 

 a network such that each coordinate passes (as nearly as possible) 

 through points corresponding to those of the former figure. It will 

 be seen that two differences are apparent. (1) The values of y 

 in Fig. 512 are large in the upper part of the figure, and diminish 



Fig. 511. Oithona nana. 



Fig. 512. Sapphirina. 



rapidly towards its base. (2) The values of x are very large in the 

 neighbourhood of the origin, but diminish rapidly as we pass towards 

 either side, away from the median vertical axis; and it is probable 

 that they do so according to a definite, but somewhat complicated, 



* It was these very drawings of Diirer's that gave to Peter Camper his notion 

 of the "facial angle." Camper's method of comparison was the very same as ours, 

 save that he only drew the axes, without filling in the network, of his coordinate 

 system ; he saw clearly the essential fact, that the skull varies as a whole, and that 

 the "facial angle" is the index to a general deformation. "The great object was to 

 shew that natural differences might be reduced to rules, of which the direction of 

 the facial line forms the norma or canon ; and that these directions and inclinations 

 are always accompanied by correspondent form, size and position of the other 

 parts of the cranium," etc.; from Dr T. Cogan's preface to Camper's work On the, 

 Connexion between the Science of Anatomy and the Arts of Drawing, Painting and 

 Sculpture (1768?), quoted in Dr R. Hamilton's Memoir of Camper, in lAves of 

 Eminent Naturalists (Nat. Libr.), Edinburgh, 1840. See also P. Camper, Dissertation 

 sur les differences reelles que presentent les Traits du Visage chez les hommes de 

 differents pays et de differents ages, Paris, 1791 {op. posth.); cf. P. Topinard, ]6tudes 

 8ur Pierre Camper, et sur Tangle facial dit de Camper, Bev. d'Anthropol. n. 1874. 



