THE GROWTH OF THE OVUM, FORMATION OF 

 THE POLAR BODIES, AND THE FERTILIZA- 

 TION IN POLYCHOERUS CAUDATUS. 



EDWARD G. GARDINER. 



While studying the segmentation of the ova of Polychoerus 

 caudatus, large numbers of these little animals were kept alive 

 in small aquaria under constant observation, and their habits 

 were carefully studied. When a number of them are placed 

 together in a small dish, after a short time most of them settle 

 on the bottom of the dish and remain quiet. There are gen- 

 erally, however, a noticeable few who keep on the move, 

 endeavoring to find a lodgment on the back of some other indi- 

 vidual. Sometimes one of the latter may remain motionless 

 and allow a pursuer to creep onto its back, but not infrequently 

 it moves off a short distance and then comes to rest again, in 

 which case the disturber follows and again endeavors to gain a 

 resting-place on its back. I have seen one of these worms 

 thus pursue others for upward of half an hour, and each time 

 just as it gained a lodgment on the back of the one sought, 

 the latter would move off. Finally, as if to get rid of further 

 annoyance, the pursued one came to the surface of the water, 

 where it swam with its ventral side up, thus preventing its 

 pursuer from accomplishing its purpose. After these observa- 

 tions had been repeated many times, it occurred to me that 

 the pursuer was endeavoring to fertilize the pursued by hypo- 

 dermic impregnation. To confirm this I have taken one of 

 these restless individuals and put it, with several others which 

 were at rest, in a shallow watch glass, where they could be 

 observed more closely. I found that after the restless one 

 gained a lodgment on another both were quiet for a short time 

 and then separated. 



More frequently the under one moved first, and then in such 

 a manner as to suggest that it had been suddenly disturbed by 

 its burden. Several times I have seen the under one suddenly 



