770 PROCEEDINGS OF THE ACADEMY OF [DeC, 



ing had gone on until the isthmus was a quarter as long as the 

 entire bud (fig. 7), it began to grow still thinner at its middle, 

 and finally, just half an hour after it first began to stretch out, it 

 broke in two and the bud fell away from the parent (fig. 8). The 

 two ends of the connecting stalk shrank back into the tissues of the 

 bud and of the parent, appearing for a time as minute points of 

 protoplasm, as in the drawing. After separation from the polyp 

 this particular bud settled down at once upon the previously free 

 or distal end, and began an independent existence (fig. 9). Other 



Fig. 9. • , Fig. 10. 



Detached larva, just settled The same four days later. Basal 



down, three days after detach- ectoderm thickened, 

 ment. 



observations, however, indicate that the usual course of develop- 

 ment is slightly at variance with this instance, and that it includes 

 a motile period of from three to four days, intervening between 

 the detachment of the bud and its settling down as a hydra, A 

 bud which was growing upon the body-wall one day would be gone 

 the next, and for some lime could not be found. Then it would 

 suddenly appear in some previously vacant spot, at a distance from 

 the polyp, perhaps in an entirely different watch-glass on the 

 bottom of the aquarium, with its tentacles just beginning to 

 appear. In one case the bud was drawn and measured when it 

 seemed to have reached its full size and to be ready to drop off. 

 This was done one evening, and the next morning no bud was to 

 be seen upon the parent polyp. Three days afterward a small 

 polyp was found upon a spot which certainly had been unoccupied 

 up to that time, according to diagrams made at short intervals. 

 This was a larva like that in fig. 10. It was measured, and 



