﻿Dec. 1856.] 



ELLIOTT SOCIETY. 



87 



In conclusion, I sum up, in connected view, the reasons which 

 induced me to treat the foregoing as really the embryonic develop- 

 ment of Oceania (Turritopsis) nutricula, and not the parasitic em- 

 bryology of an iEginoid Medusa. 



1st. When larvae are present in the bell of Turritopsis nutricula, 

 the ovaries are either empty, or nearly so. Showing that all or the 

 greater part of the ova have been discharged. 



2d. That these hydroid larvae are to all appearance willingly fed 

 by the presumed parent Turritopsis. 



3d. That the number of tentacula, in the oldest larval Medusae, 

 was the same as that observed in the youngest and smallest Turri- 

 topsis found — namely, eight. 



4th. That these tentacula were, in the main, identical in structure 

 in both the larval Medusae and the adult Turritopsis, with the ex- 

 ception that those of the latter possessed ocelli which were wanting 

 in the larvae. 



5th. That the supposition which takes it for granted, from the cir- 

 cumstances, that Turritopsis is really the parent of these larvae, is 

 the most natural explanation of the facts, isolately considered. 



6th. That it is already known that, in Tubularia, the young 

 hydra? are developed in the same manner, as these larvae are de- 

 veloped in Turritopsis — namely, under the protection of the 

 Medusa-disk. 



7th. That there is yet no certainly-known instance of the para- 

 sitic development of one Medusa, within the bell-concave of 

 another. 



EXPLANATION OF THE PLATES. 4, 5, 6, 7. 



PLATE 4. 



Fig. 1 to 6. — Oceania (Turritopsis) nutricula in several positions and states of ex- 

 pansion. Fig. 3. 1. 4. 5. are protile views, the tentacula being fully stretched 

 out in fig. 5 — tightly curled and knotted together in fig. 3, and in fF. 1 and 4 

 they are seen at intermediate stages of expansion. Ff. 2 and 6 are views 

 from above. In fig. 2. the tentacula are fully extended, in fig. 4. contracted. 

 In fig. 1, and fig. 2, the following are the references of the letters : 

 a. the upper hyaline portion of the proboscis. 



d. the four lips or oral leaflets, two of which in fig. 2 are so elongated and 

 turned upwards as to appear on the upper portion of the lateral surface 

 of the proboscis. 



c. the four vertical chymiferous tubes. 



A, the four opaque sexual lobes. 

 Fig. 7, — A transverse diagrammatic section of the upper hyaline portion of the 



