50g Philippine Journal of Science *•» 



to form planes of contact with the walls of opposite and neigh- 

 boring gonidia. The thickening of the inner wall of the goni- 

 dium, sufficient for contact with the walls of the neighbors, 

 extends outward to about the equatorial plane of the gonidial 

 protoplast. From this region outward the walls separate and 

 rapidly shade off in thickness, leaving an intercellular space 

 between the gonidial walls and the walls of the somatic layer. 

 The anterior walls of the anterior quartet of gonidia round out 

 into the anterior intercellular space of the coenobium. 



The terete condition of the coenobia under the margins of the 

 cover glasses seems to be due to the absorption of atmospheric 

 moisture during the storage of the preparations. The first water 

 absorbed seems to be taken up by the cell membranes, particu- 

 larly by the intralamellar substance of the somatic and gonidial 

 cell walls, and by the substance in the intercellular coenobial 

 cavity. After sufficient water has been absorbed for the com- 

 plete expansion of the cell walls, additional water absorbed seems 

 to be taken up by the protoplasm and by salts in the vacuoles, 

 rendering the specimens unsightly. 



The form and extent of the membranes of the sexual repro- 

 ductive cells I have not been able to determine. 



The details of the structure of the somatic protoplasts as they 

 occur in the living and the fixed material are yet to be studied, 

 and will not be taken up here. 



The full history of the segmentation of the gonidia and the 

 metamorphosis of the embryos will likewise be left for future 

 study. The material on the type slide was purposely fixed at an 

 hour when the characteristic stages of the embryos were present 

 in abundance, with the result that stages of segmentation of the 

 gonidia are lacking in this batch of material. 



The most distinctly peculiar features of the ontogeny of this 

 species appear in Plate II, figs. 13 and 15. These are both from 

 slide 1 of the pond F material. Fig. 13 shows a specimen (No. 

 27) in which the youngest of seven embryos, in the left upper 

 quarter, is in the bowl stage with the gonidia perched on the 

 rim of the bowl. The older embryos are in the bullet stage, 

 the four in the center and the right upper quarter presenting 

 side views, and the two lower ones presenting almost rear polar 

 views. In all of these bullet embryos, except the nearer one 

 showing a side view, the gonidia are closely packed, and in the 

 exceptional case they have begun to separate. 



The bullet embryos are shown on a larger scale in Plate II, fig. 

 15, a view of a specimen (28) containing six embryos and one 



