HYOBRANCHIAL APPARATUS OF SPELERPES 545 



and cuts off the second basibranchial, and from that position 

 radiates until only the first ceratobranchials and the gradually- 

 ossifying osthyreoideum are left. 



Almost all of the cartilages show, to some extent, the phe- 

 nomenon of becoming adapted to their new functions by the 

 principle of degeneration and new growth. In the case of the 

 ceratobranchials and the proximal end of the first epibranchial 

 which is retained through adult life, it is seen in a slight de- 

 generation around the periphery, to give them the slenderness 

 characteristic of the adult skeleton. 



The principle is even more marked in the case of the basi- 

 branchial, and most evident of all, in that of the ceratohyals. 

 The basal piece, during the metamorphic period, loses its anterior 

 end and attains the flattened ventral surface of the adult by the 

 process of degeneration of old tissue (figs. 34 and 38), and be- 

 comes broadened by the lateral shelves which first appear in 

 stage II as thickenings in the perichrondrium, and gradually 

 becomes cartilaginous (figs. 38 and 44). The ceratohyals lose 

 their connection with the basibranchial and assume their more 

 dorsolateral position and adult form by the degeneration of the 

 anterior end, and dorsal, medial, and ventral surfaces an- 

 teriorly, and of the whole periphery more posteriorly, and by 

 the outgrowth of new tissue laterally, especially at the posterior 

 end where the 'hook' which becomes attached to the quadrate 

 is almost wholly new. 



These processes go on so quickly during the true metamorphic 

 period that at the end of that time all the changes are indicated 

 and only final consumption by phagocytes of the already de- 

 generating matrix, and fuller chondrification of the new parts 

 already laid down, is necessary before the final adult condition 

 is reached. 



2. Muscles 



The study of the metamorphosis of the hyobranchial muscles 

 shows quite as important results as does that of the transforming 

 skeleton. I have not yet worked out the more minute details 

 of the histological phenomena, but in the main, I find results 



