OF THE TELEOSTEAN FISH SEBASXES MARIN US. 



507 



has not yet appeared. The branchial bars occupy a rather 

 advanced position. They form a kind of ridge on the iloor of the 

 mouth, the copula communis being at a higher level than the gill- 



Text-fiffure 5. 



Text-figure 6. 



C.H.- 



C.Com. 



Stage 3. Dorsal view of 

 branchial bars. 



Stage 3. Dorsal view of 

 chondrocranium. 



bars which slope downwards and backwards in relation to it. 

 The interior of the mouth is thus in the form of an inverted V 

 when viewed in transverse section. 



d. Stage 4. The 25 mm. Stage. 



The chondrocranium may now be looked on as fairly complete 

 (text-figs. 7, 8, and 9). A certain amount of ossification has 

 taken place. As already mentioned I was unable to procure any 

 specimens between this and the 5'5 mm. stage, and at first glance 

 it would seem that the gap is so large that it would be a matter 

 of difficulty to connect the two stages with any profit. However, 

 by a careful study of the complete chondrocranium and by 

 analogy with the changes which take place in other forms, it is 

 possible to reconstruct from a general point of view the processes 

 which bring about the conditions found in the present stage. 



The ethmoid region of the mature chondrocranium of Sebastes 

 (text-fig. 7) bears a strong resemblance to that of Sahno, and 

 there can be little doubt that it arises in much the same manner. 

 In the 25 mm. stage it consists of a substantial mass of cartilage 

 roughly triangular in shape when viewed from the side. The 



