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elasmobranchs, that it is taken up by the embryo. It is probable 

 that it is appropriated via gills (which may become trophone- 

 mata, as shown by Wood-Mason, Alcock, Haswell and others), 

 and gut. This stage is of further interest from the stand- 

 point of the morphology of the chimojroid head, for it demon- 

 strates that the autostylous character of the skull is secondary, 

 as had indeed been surmised from the time of Johannes Miiller. 

 As indicated in Fig. 19, from a drawing of a wax-plate model, 



FIG. 19. Skull of embryo shown in Fig. 6. After wax -plate model, 

 palato-quadrate is shown fusing with the cranium at the points A and B. 



The 



the skull in this stage shows the upper jaw (palate-quadrate) 

 still separate, although even at this early stage its fusion with 

 neighboring cranial cartilage is taking place at both its anterior, 

 and posterior borders, A, B. Conspicuous in all early stages 

 is the disproportionate size of the anterior and posterior body 

 regions ; head and anterior trunk are large, posterior trunk and 

 tail dwindle away narrowly, the latter, however, attaining ex- 

 treme length. These characters, together with the great size of 

 the eyes in embryonic stages, are clearly in the line of preparing 

 the young fish for the conditions of deep-water living. 



Conclusions. The mode of development of CJdinccra affords 

 evidence, I conclude, in support of the following theses. 



I. That sharks and chimaeroids are closely related geneti- 



