Notes on Medusce of the Western Atlantic. 145 



locate. I had not entertained any idea of finding a large and conspicuous 

 hydroid, but the minute proportions of the creature when finally discovered 

 surprised me. The polyp, growing singly, was so exceedingly delicate that 

 it was almost invisible to the unaided eye. Only one specimen of the entire 

 number that came to light, over a dozen in all, was large enough to be at 

 all readily seen without a lens. This, though slender and transparent, meas- 

 ured 1.5 mm. in height. It is no wonder, then, that this form has not been 

 a familiar sight to visitors in these waters ! 



During the time that the search was being carried on in the moat, careful 

 watch was being kept over the medusae which were brought into the labora- 

 tory every day. Only one individual was found in which the gonads showed 

 any sign of activity. In this, a single spherical mass appeared upon the 

 manubrium, above the gastric enlargements. This medusa was kept under 

 frequent observation for some days, but the only perceptible change was 

 an increase in the size of the egg, if such it was. The specimen disappeared, 

 finally, without throwing any light upon the laying or development of the egg. 



Filiform tentacles. The absence of tactile hairs from the tips of the 

 lower row of tentacles has been mentioned. The function of these pro- 

 cesses, or " false tentacles," as Hincks 1 terms them, is problematical. It does 

 not seem to be at all certain that they are intended to perform the function of 

 tactile organs, inasmuch as their sensitiveness does not exceed that of the 

 adjacent parts. Hincks says : " Their function seems to be to give notice of 

 the presence of animalcules or other prey. If anything touches them, the 

 head and upper arms are instantly bent towards it." I tried to find out 

 whether this same reaction occurred in our species, and found that it did. 

 But it did not make any difference whether the stimulus was applied to 

 the tip end of the process, or to some other part of it, or to the column of 

 the polyp nearby. It is likely that in the other species the tactile sense is 

 more localized. 



Feeding reactions. The same eagerness in the presence of food which 

 was noted in the medusa also characterizes the hydroid. The column of the 

 polyp stands up stiffly and without any sign of life when there is no prey 

 near. The capitate tentacles around the mouth droop a little at the tips, 

 and the filiform tentacles below are straight and stiff. But let the smallest 

 speck of an animalcule come along and touch the polyp, and it suddenly 

 becomes flexibility itself. The column bends and twists, the oral tentacles 

 reach after the prey, and even the slender tentacles below manifest signs of 

 life. Plate 2, figure 7, is a drawing made to show the attitude of one of 

 the polyps at the instant that a small worm, which had become partially 

 fixed to the column by the nematocysts, made good its escape. 



Reproduction. I was unable to see that any definite gonophores were de- 



1 Hincks, loc. cit., p. 64. 



