426 JAMES ERNEST KINDRED 



MATERIAL AND METHODS 



The description of the chondrocranium of Syngnathus fuscus 

 is based upon the study of serial sections through the head regions 

 of embryos from 6 mm. to 15 mm. in length. For purposes of 

 orientation and comparison, reconstructions were made in wax 

 of the chondrocrania of the 8-mm. and 12-mm. embryos, which 

 represent typical stages in its development. - 



Male pipe-fish carrying young in the brood pouch were kept 

 in laboratory aquaria, and a few embryos from each fish were 

 taken out and fixed daily. It is impossible to state the exact 

 age in hours of the embryos, because in all cases where they 

 were collected, development was advanced at least as far as the 

 closure of the neural tube. The 12- to 15-mm. stages were 

 larvae capable of caring for themselves. These were the oldest 

 animals that I was able to raise in the laboratory, because their 

 resistance is very low to changes in the environment at this age, 

 the critical period when the yolk sac has just been absorbed. 



The material for study was collected at Woods Hole during 

 the summer of 1919 by the Supply Department of the Marine 

 Biological Laboratory. 



THE CHONDROCRANIUM OF THE 8-MM. STAGE 



In embryos of Syngnathus fuscus younger than the 8-mm. 

 stage of development, the chondrocranium has not been defini- 

 tively laid down. The cranial flexure is marked and the head 

 region has not straightened out. In a 6-mm. embryo the vis- 

 ceral arches are formed of dense mesenchymatous masses; 

 procartilage tracts are present ventrolateral to the otic vesicles, 

 but were not observed ventral to the brain or lateral to the 

 notochord. Since chondroblasts are not present except in these 

 regions, it is probable that the chondroblasts which later form the 

 basis cranii are proliferated from the visceral-arch masses of 

 mesenchyme. 



