272 CHAS. W. HARGITT, 



Life History of the Plaimla. 



Ill general the life liystory of the Eudendridae is quite similar 

 to that of other Hydromedusae, only those features which are more 

 or less distinctive will be noticed. In the general shape there is 

 nothing peculiar. When first liberated they are elongate pyriform, 

 becoming much more slender after a few hours or a day of the free- 

 swimming condition. The planula of Eudendrium is from the first 

 abundantly ciliated, much more so than that of Pennaria or Clava. 

 By a curious oversight, which I desire to correct in this connection, 

 the planula of Eudendrium which was under observation at the same 

 time with those of Pennaria, of both of which drawings were made, 

 that of the former was inserted in the paper on the latter, fig. 7, 

 tab. 1, to which reference may be made instead of its reinsertion in 

 the present. 



The free swimming period is comparatively brief, rarely exceeding 

 two or three days, usually less. At first the movements are relatively 

 rapid, particularly when compared with those of Pennaria which are 

 quite slow. A point of considerable interest in this connection is 

 that of the heliotropism of the planulae. This is specially marked 

 daring the first few hours following their escape from the gonophores. 

 Their liberation seems to be chiefly during early midday from colonies 

 brought into the laboratory during the morning. In those collected 

 during the late afternoon very few planulae were set free. When 

 liberated from large colonies at the height of the breeding season 

 their numbers were large and they promptly swam directly toward the 

 strongest light with great uniformity. By interposing a dark screen 

 between this source of light and allowing another from the opposite side 

 to operate upon the aquarium, there was an almost instantaneous 

 response, the entire number almost without exception facing directly 

 about, like a body of soldiers at command, and moving without deviation 

 in the opposite direction, that is, toward the second source of light. 

 The experiments were so varied and repeated as to leave no shadow 

 of doubt concerning the general fact of the postively heliotropic 

 character of these larvae. It rapidly declines, however, during later 

 life, tho still persists even in the hydroids themselves as numerous 

 experiments by Loeb and others have shown. 



Abnormalities. Of these I have found comparatively few, 

 most conspicuous among which is that of the bifurcation of the planula 

 at the (usually) oral end. This feature was quite common in the 



