272 



Prof. E. W. MacBride. 



correctness of his views has been often questioned even by Theel.* 

 It affords me much pleasure to be able to completely confirm Bury's 

 views ; every stage of the process of the transverse division of the 

 ccelom has been observed by me. 



At 19 20 days the ectodermic invagination on the left side of the 

 larva has become flask-shaped, and its floor is now in close contact 

 with the hydroccele. The latter has now taken on the form of a 

 flattened pentagon (fig. 6). It never has the form of an open hoop, so 

 characteristic of the corresponding organ in Asteroidea, Ophiuroidea, 

 and Holothuroidea. 



FIG. 5. Diagrammatic Longitudinal Section of a Larva about 23 days old. 



Names as before. In addition, a.cil.ep., anterior ciliated epaulette ; p.cil.ep., 

 posterior ciliated epaulette ; ep.f., epineural fold ; ped., apical pedicellaria ; 

 t., primary tube-feet of the Echinus. 



About 21 days the rudiments of the last Pluteus arms (the 7th and 

 8th) appear, and the pentagonal hydroccele sends out at its corners 

 five projections which are covered by corresponding elevations of the 

 ectoderm. These are the rudiments of the radial canals of the adult, 

 arid their terminations form the five primary azygous tube-feet of the 

 young Echinus which correspond to the ocular tentacles of an Asterid. 



* Loc. cit. 



