ZYGODACTYLA GROENLANDICA. 105 



these rudimentary tubes are mere threads, running a short distance, 

 and then suddenly terminating, or tapering gradually to a point. In 

 the latter part of June, or early in July, the Zygodactyla? are all in this 

 condition, while later in the season, in August and the latter part of 

 September, they attain their full size, all the chymiferous tubes being 

 about equally developed. The lips of the actmostome are so read- 

 ily movable that the outline of its edge will assume the most varied 

 shapes, the opening being either concentric and perfectly circular, 

 or else thrown entirely to one side, or assuming a pear-shaped form, 

 closing at another time like the actinostome of an Actinia, and then 

 suddenly spreading into a pentagonal opening ; or the membrane of 

 the digestive cavity is expanded to its fullest capacity, extending far 

 below the circular tube, and leaving but a very small elliptical acti- 

 nostome, from which a sheaf of long, slender, highly fimbriatecl, lance- 

 olate lips are suspended. 



Notwithstanding the facility with which this species is kept alive, I 

 have never succeeded in raising the eggs, as is so easily done with 

 Tima and Melicertum, and can therefore add nothing to the observa- 

 tions of Wright on the Hydrarium of ^Equorea vitrma. 



Among the numerous young Eucopida?, daily examined, are fre- 

 quently found exceedingly small Medusa?, not larger than the head 

 of a pin, which I suppose to be the young of Zygodactyla. They 

 resemble the Eucopida?, but differ in having 

 rather more slender tentacles, and a very 

 peculiar gelatinous projection of the disk, at 

 the base of which are situated four round 

 genital organs (Fig. 15G) ; there are four 

 chymiferous tubes opening into a large cav- 

 ity, leading into a slightly pendent stomach, 

 exactly as would be the case in a Zygodac- 

 tyla, if we were to reduce the chymiferous 

 tubes to four, and make the genital organs 

 round. The youngest Medusa? have already twenty-four tentacles, 

 and the next size, scarcely larger, forty-eight ; from this large number 

 of tentacles, as well as the peculiar projection of the gelatinous disk, 

 and the large cavity from which the chymiferous tubes take their 

 origin, I have but little doubt that they are the young of ^Equoricla?, 

 probably of our Zygodactyla. The small size of these Medusa?, coupled 

 with their habit of living at the bottom, till late in the fall, when 

 they make their appearance as full-grown Medusa?, will readily account 

 for their having escaped our notice thus far. These young ^Equorida? 

 are quite common early in June ; their further development could not 

 be traced, as they do not thrive in confinement. 



Fig. 156. Young Zygodactyla, greatly magnified. 

 NO. n. 14 



