368 Prof. Allman on the Hydroid Zoophytes. 



In the specimens examined, each capsule contained but a 

 single Medusa, which sprang from the side of a blastostyle, and 

 occupied the greater part of the capsule. 



There can, I think, be no doubt that some minute Medusa? 

 which I found free in the phial containing my specimens of L. 

 tenuis, and which, so far as comparison was practicable, closely 

 corresponded with those which lay contracted in the interior of 

 the capsules, had been liberated from the present zoophyte. 

 They were provided with a deep umbrella,, having its transverse 

 and vertical diameter each equal to about jfa of an inch. The 

 form of the umbrella is rendered peculiar by the abrupt narrow- 

 ing of its summit. The roof of the bell descends as a conical pro- 

 jection into the axis, and from the truncated apex of this inverted 

 cone there hangs a conical manubrium, whose mouth is furnished 

 with four tentacles, each terminating in a spherical cluster of 

 thread-cells. 



Four gastrovascular canals take their origin in the base of the 

 manubrium, and, after ascending along the sides of the conical 

 projection from the roof, descend in the walls of the umbrella to 

 open into the circular canal. At the point where each radiating 

 canal enters the circular canal there is a bulbous dilatation, from 

 which two marginal tentacles are given off; and in the middle 

 point between each of these bulbs there is a similar, though 

 smaller, bulbous dilatation of the circular canal, which gives 

 origin to a single tentacle. The tentacles have their endoderm 

 presenting the usual vacuolated condition ; and the thread-cells 

 of their ectoderm are uniformly distributed over their surface, 

 showing no tendency to an arrangement into distinct groups. 

 The velum is moderately wide. There are no lithocysts or 

 ocelli. 



In the further development of the Medusa, the marginal ten- 

 tacles are probably multiplied in each group ; at least, in one 

 specimen I found three tentacles springing from a single bulb. 

 The Medusa also appears to belong to a type in which the gene- 

 rative elements are developed in the walls of the manubrium, 

 thus affording an exception to the usual condition of the Medusa? 

 in the Campanulctriadce, where the generative elements are formed 

 in special bodies which bud from the radiating canals*. 



* In Sarsia and its allies the generative elements are formed, as is well 

 known, in the walls of the manubrium, where they lie between the endo- 

 derm and ectoderm, a position quite similar to that assumed by them in 

 the sporosac of Clava, Hydractinia, certain species of Coryne, of Laomedea, 

 Sertularia, &c, as well as in the Medusa-buds of Eudendrium ramosum, 

 Van Beneden, and certain other species of Coryne. 



In Laomedea dichotoma, L. geniculata, &c, the generative elements are 

 never formed in the manubrium of the Medusa bud, but in peculiar bodies 

 seated on the course of the radiating canals. Now these bodies, at least in 



