242 WM. A. KEPNER AND JOHX F. BARKER. 



the bases of the tentacles. The third time it came to lie over 

 the mouth of the Hydra, the latter began an effort to ingest the 

 Microstoma (Fig. i). First the Hydra's peristome opened up 

 against the ventral side. This region of the peristome did not 

 fix the Hydva to the Microstoma, for the mouth of Hydra glided 

 posteriory along the ventral side of Microstoma and around 

 its posterior end as indicated by the arrow in Fig. 2. When 

 the widely expanded peristome of Hydra had come to be ap- 

 plied over a great part of the dorsal and lateral surfaces of the 

 Microstoma, the Hydra pressed the latter between its peristomal 

 bell and its body and appeared to have the worm in a very 

 serious position (Fig. 3). But from this embrace the Mic- 

 rostoma soon glided. As it escaped it showed a ruptured region 

 of its body. This wound healed in a little while and then Mic- 

 rostoma went back and played along the surfaces of Hydra's 

 body. The next time it came into the tentacular zone of Hydra, 

 the polyp succeeded in grasping the Microstoma head-on and 

 forthwith ingested it (Fig. 4). Since, therefore, Microstoma 

 incurs a greater danger in seeking out Hydra than it does when 

 it feeds upon small annelids, Crustacea and other small animals 

 and plants and since, further, it does not appear to seek Hydra 

 primarily for food as will be shown later, the inference is strong 

 that it is seeking Hydra for some unique end. 



Microstoma ABLE 10 DRAW NEMATOCYSTS FROM ITS BODY 

 WHEN WOUNDED BY Hydra. 



Moreover, Microstoma seems to have developed an adaptive 

 secretion by its epidermal glands that may be taken to be either 

 rhabditic glands or the homologues of such glands which are 

 found in other rhabdocoeles. The following observations indi- 

 cate the adaptive functioning of these glands. February 15, 

 1917, a Microstoma was placed with a small Hydra fusca. The 

 Microstoma began playing about the five tentacles. Immediately 

 the Hydra firmly grasped it between its tentacles (Fig. 5). The 

 Microstoma escaped from the Hydra's embrace. As it swam 

 clear of the polyp, two mucous masses were to be seen, one at 

 the posterior end and one on the right side. (Fig. 6). The 

 lateral mass grew and as it grew drew the two enclosed nemato- 



