vol. i.] "RitU r— Davis. — Enteropnetista. 1 85 



this is developed from the wall* of the proboscis eoelom, and, as 

 we have pointed out above, the bilateral thickening which 

 initiates the differentiation of these muscles is probably the verj 

 earliest step toward metamorphosis. 



Although we were unable, with the aquarium facilities at 

 command, t<> carry the development of the young enteropneusl 

 through the stages of most importance to the standing problems 

 of chordate phylogeny involved, and consequently are compelled 

 to leave this whole matter aside for the present, we deem it best 

 to touch two points from this standpoint. We would first 

 direct attention to the tardiness with which the axial skeleton 

 of the adult state comes into existence in this species. (By 

 the axial skeleton we mean the notochord plus the nuchal 

 rod and its two limbs, associated with the notochord.) Al- 

 though in the most advanced stages obtained, the animal had 

 become distinctly an enteropneust, the three regions of the body 

 being set off, the first pair of external respiratory stigmata and 

 the neural canal both being present, there was still no positive 

 intimation of any of the skeletal parts. With this tardiness in 

 the development of the axial skeleton, there is a corresponding 

 tardiness in the development of the musculature of the collar. 



It is instructive to observe the movements of the young ani- 

 mal at this stage. While the proboscis is highly active, the 

 radial muscle plates of this part being already well developed, 

 practically no motion takes place in the collar or the abdomen. 

 This we regard as of importance in connection with the 

 effort of one of us, Hitter, '02, to correlate locomotion and the 

 locomotor musculature in the adult with the axial skeleton. 



The other point which we touch we are led to by the remarks 

 in the preliminary communication of Ritter, '94, relative to 

 the possible existence of an endostyle in this species. After 

 describing a thickened ciliated baud of epithelium along the floor 

 of the esophagus, and a somewhat similar band joining this on 

 the floor of the stomach, it was remarked that it is "highly 

 probable that the esophageal baud is, functionally at least, an 

 endostyle"; and further, that "whether it be homologous with 

 that orgau in the chordata, is quite another matter." We regret 

 that in spite of careful attention to the point, we are not yet in 



