100 



HALOPSIS OCELLATA. 



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

 Jig. 143 earlier stages known, they would readily have 



been mistaken for different ages of the same 

 species. 



The first species, Halopsis 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 tuljes. The tentacles ai'e 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, t, Fig. 



14G) bulge out jii'ominently 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 Medusas are exceedingly sluggish in their 



movements ; they are colorless, the genital organs ' '' " 



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



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

 Fig. 148. 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 



Fii;. 143. Portion of the disk of Halopsis ocellata, seen from the abaotinal pole, soniewliat 

 redueed. 



Fi(j. 144. Cavity from which tlie cliymiferoiis tiilics railiato. /!, opcnin;; of actinostome ; c, 

 chymiferous tube ; b, connecting foUl between the point of attachment of two chymiferous tubes ; 

 /, lips of actinostome. 



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



