﻿Dec, 1856.] 



ELLIOTT SOCIETT, 



^3 



its original position. Certainly this hold is not maintained by 

 suckers, and it is more than likely that is due entirely to the 

 action of filifereous cells, hut I have not seen the threads. The 

 small rounded prominence just above the otolithic cyst on each of 

 the muscular lobes, which has already been noticed as probably a 

 rudimentary tentaculum or representative of an ocellary or nervous 

 bulb, appears to be in connection with the marginal cord, and 

 consists of round cells somewhat larger than those in their vicinity, 

 (ff. 39, 40, 41, p.) I did not distinctly recognize in them the 

 structure of the thread cells, but they may be such in process of 

 development. I saw, however, nothing in them which counten- 

 ances the supposition of Kolliker that the corresponding parts in 

 Stenogaster might be sexual organs, independently of which, anal- 

 ogy would rather bear out the opinion I have expressed above, of 

 their homology to the "tubercules ayant la forme d'un petit mame- 

 $on," described by Milne Edwards in vEquorea. 



We may now sum up the various stages of this embryonic de- 

 velopment as follows : 



First stage — an un-tentaculate, club-like, proboscidian larva. 



Second— a bi-tentaculate larva with long neck, digestive cavity, 

 and oesophagus, but imperforate mouth. Here gemmation begins 

 on the posterior surface. 



Third— Four tentacula, mouth sometimes assuming a bi-labial 

 form. 



Fourth — Medusa disk begins to grow beneath the tentacula, and 

 four new tentacula begin to sprout. Shortly two otoliths are seen 

 in eaoh of the incipient lobes of the disk. 



Fifth — The hydra assumes the form of a proboscidian Medusa, 

 with octagonal stomach, a scalloped margin, eight tentacula, four 

 large and four small, recessed from the margin of the disk, ei^ht 

 muscular lobes, and eight otolithic vesicles, above each of which 

 is a rudimentary knob. At this stage the Medusa escapes from the 

 mother's disk. 



Seventh — The proboscis disappears, and the digestive cavitv 

 assumes the form known in the JEginida?, with the exception that 

 it has no sexual organs. 



With regard to the number of lobes, tentacula, etc., there are 

 occasional monstrosities, both by defect and excess, and I have 

 even observed two otolithic vesicles on the same muscular lobe, a 

 phenomenon sometimes observed in the iEginida?. 



Comparing now the development of Turritopsis nutricula with 



