100 HALOPSIS OCELLATA. 



which are so closely allied that, were not the complete history of their 

 Fig . 143 earlier stages known, they would readily have 



been mistaken for different ages of the same 

 species. 



The first species, Hatopsis ocellata, would 

 at first glance be taken for a Stomobra- 

 chium ; on examination we find that the chy- 

 miferous tubes take their origin in clusters 

 of three to five (in adults), radiating, like the 

 spokes of a fan (Fig. 143), from a large cross- 

 shaped cavity (Fig. 144), from which hangs 

 down a short digestive cavity, terminating in 

 four lips. When seen in profile, the disk is 

 quite flat, regularly arched, the genital organs 

 extend nearly to the circular tube (Fig. 145), 

 occupying almost the whole length of the 

 chymiferous tubes. The tentacles are very 

 numerous, and capable of great expansion and 

 contraction (Figs. 143, 145) ; there are as 

 many tentacular cirri as tentacles (c, Fig. 146) ; they are long, slender, 

 of uniform diameter ; the main tentacles (t, f, Fig. 

 146) bulge out prominently immediately at the 

 circular tube, tapering very rapidly. The com- 

 pound eyes are large (e, Fig. 146); the granules in 

 them are arranged in two rows, from six to seven 

 in each row (Fig. 147) ; the structure of these 

 compound eyes is similar to those of Tiaropsis. 

 These Medusa? are exceedingly sluggish in their 

 movements ; they are colorless, the genital organs 

 having a slight grayish tinge at the time of spawning. Found at Nahant, 

 from July to September, quite commonly. In young specimens, meas- 



Fi g . 145. uring not more than an 



inch in diameter, there 

 are only four chymif- 

 erous tubes (Fig. 148), 

 uniting in the form of 

 a cross ; there are no 

 signs of genital organs ; 

 the shape of the disk is somewhat more hemispherical than in the 



Fig. 143. Portion of the disk of Halopsis ocellata, seen from the abactinal pole, somewhat 

 reduced. 



Fig. 144. Cavity from which the chymiferous tubes radiate, d, opening of actinostome ; c, 

 chymiferous tube ; ft, connecting fold between the point of attachment of two chymiferous tubes ; 

 Z, lips of actinostome. 



Fig. 145. Profile of Halopsis ocellata ; natural size. 



