54 SCIENCE PROGRESS 



since it shows that a record of the changes which transformed 

 a regular sea-urchin into a Spatangoid are indicated in the 

 post-larval development of the latter. Thus, although it is 

 devoid of teeth in the adult, five dental sacs are formed in the 

 larva ; the intestine in the young image is thrown into a re- 

 verse coil as in the regular Urchin ; its spines (with certain 

 exceptions) are similar to those of the regular Urchin and so 

 on. The madreporite vesicle originates from a dorsal out- 

 growth of the right anterior ccelom. The left anterior ccelom 

 is modified into an axial sinus which does not develop and is 

 vestigeal in the adult. 



Other papers include : Crozier, " The Amount of Bottom 

 Material ingested by Holothurians (Stichopus) " {Jour. Exp. 

 Zool. vol. xxvi. No. 2, July 191 8). 



Two points in the embryology of Peripatus as described by 

 Sedgwick have led to considerable discussion, and the author 

 himself laid a great deal of stress on them in his subsequent 

 writings ; these have been reinvestigated by Glen ; " A Revision 

 of Certain Points in the Early Development of Peripatus capensis" 

 {Quart. Jour. Micro. Sci. vol. lxiii. Part 2, August 191 8). It 

 has been found that in the early stages of development there 

 is no doubt as to the presence of cell walls — a fact denied by 

 Sedgwick. Again, this author maintained that the whole of 

 the nephridium was mesodermal in origin, but Glen has shown 

 that, as in Annelids, the tube is completely ectodermal and 

 only the funnel is mesodermal. Thus the structure of the 

 excretory organ in Peripatus is homologous with that in the 

 Annelids. 



11 The Segregation of the Germ-Cells in Tricho gramma 

 evanescens " has been described by Gatenby {Quart. Jour. Micro. 

 Sci. vol. lxiii. Part 2, 191 8). The author previously described 

 a number of the developmental stages in this form and has now 

 been able from further material to add to that, the present 

 account of the cytological changes involved in the segregation 

 of the germ-cells. The former description of a cloud of granules 

 constituting the germ-cell determinant, which seem to appear 

 spontaneously in the egg before the extrusion of the first polar 

 body, is confirmed. These granules are partly and perhaps 

 even entirely composed of cytoplasmic material and their 

 function is nutrimental. There is an early separation between 

 germ-cells and somatic cells. It seems now to be an estab- 



