26 RALPH E. WAGER. 



of being so constituted. Usually within two days the embryo 

 falls from the parent and its point of attachment is then marked 

 only by the bowl-shaped portion of the shrunken ectoderm by 

 which the egg was originally covered. 



No study was made of the processes concerned with the 

 further development of the embryo and of the cytological changes 

 involved in the transformation of the embryonic layers into the 

 definitive ectoderm and entoderm, nor of the further changes in 

 the pseudo-cells. That marked changes must take place be- 

 comes evident when one considers that in the ectoderm there 

 must be developed muscle and nerve cells, interstitial cells and 

 nematocysts, while the pseudo-cells are to be absorbed and 

 utilized by the entoderm cells. It was found that embryos 

 would develop and give rise to young Hydra in about three 

 weeks. This, of course, was at the temperature of the laboratory. 

 At the time of first appearance from the shell they are possessed 

 of four short tentacles, which later increase to six or more. All 

 traces of the pseudo-cells have disappeared by the time of the 

 completion of the definitive ectoderm and entoderm. 



General Discussion. 



As to the true nature of the growth of coelenterate eggs, two 

 views have long been prevalent. One, commonly known as the 

 amoeboid theory, is so denominated on account of the striking 

 likeness of the growing egg to an amoeba — this likeness lying in 

 the amoeboid-like movements in its migrations from one tissue 

 into another ; in that it often possesses pseudopodial processes like 

 those of an amoeba ; and more remarkable still, frequently engulfs 

 neighboring cells much after the fashion of an amoeba taking in 

 food particles. The opposing theory disavows the likeness, 

 maintaining that the egg grows by the dissolution of the cell 

 walls between the egg and the cells contiguous to it, and that 

 this process with its resulting conditions has no likeness to true 

 amoeboid activities. 



The former view was first suggested by Balfour ('80) and up- 

 held by Weismann ('83), Metchnikoff ('86), Brauer ('91) and con- 

 ditions apparently supporting it have been described by many 

 more recent writers. Doflein ('97) was the first to publish ob- 



