310 bulletin: museum of comparative zoology. 



would be one or two free broken ends for each piece, but one does not 

 find it so. Occasionally a single free end may be found but scarcely 

 ever two free ends on the one piece. 



In the case of the growing end of the stolon it appears that since 

 there is no longer any inducement to continue in the same general 

 direction in which growth has previously taken place, on account of 

 the lack of support, the growth is completed by producing a zooid 

 which thus terminates the stolon and leaves no free growing end. The 

 lack of free broken ends seems bewildering at first and it seems per- 

 missible to conclude that here is something new^ in hydroids, viz: — 

 colonies developing from planulae at the surface of the high seas, for 

 how could so many colonies, perfect ones at that, appear if they had 

 been broken away from their regular support. Further examination 



Fig. 74. — Clytia cylindrica. 



brings out the fact that regeneration is responsible for the deception, 

 but conditions must be very favorable for such regeneration since in 

 almost every instance a zooid is growing out from the broken end and 

 all are in good condition. In many cases the regenerated portion is 

 so nearly equal in size to the original part, both in the perisarc and in 

 the coenosarc, that it is difficult to detect the junction and hence the 

 deception is complete. In other cases the regenerated part is suffi- 

 ciently smaller to be readily noticed. 



Besides the zooids that grow out from the broken ends, others 

 appear to have developed in the regular way after the separation from 

 the support, as, instead of coming off regularly in the one direction, 

 they may come off on any side of the stolon to make the colony de- 

 cidedly irregular (Fig. 73). Commonly when a straight piece of 

 stolon regenerates, a zooid grows out from each end in line with the 

 stolon itself, while the zooids previously attached were at right angles 



