ALCYONELLA. 115 



ligaments being either ruptured, or having lost their hold, by dissolution 

 of the substance to which they were affixed. 



Trembley, I think, represents descending spiral organs in his Polypes 

 a pannaches, which are certainly Alcyonellce. I have never had any speci- 

 mens exposing a similar structure. Whether there be not besides the re- 

 ceptacle of aliment, organs in all, separately imparting the benefit of nutri- 

 tion received by the hydra to the polyparium or common mass below, de- 

 serves investigation. The descending organs of the Lobularia are very 

 conspicuous. 



The hydra of this paragraph is very sensitive of the presence of light, 

 and the influence of the atmosphere. Under genial temperature the body 

 is protruded far, and the head is so much expanded, as almost to appear 

 flattened. But the animal contracts in the dark ; and during cold weather 

 it becomes languid and inactive. 



These are general characteristics of the hydrae of this section. Also 

 the whole Lunatellce constitute a nocturnal race. It is then that they are 

 most amply unfolded, to enjoy the renovated medium wherein they dwell. 



Limpid water, as already said, does not seem adapted for the support 

 of any zoophytes, though its freshness is always important. Their food is 

 undoubtedly eliminated from the muddy matter so often suspended, where- 

 of the hydra? collect a surprising quantity. In the species which has just 

 come before us, a dark internal mass occupies the whole intestinal canal 

 of the hydra, descending farther than the eye can reach it amidst the mass 

 below. Amidst this also, the point of divergence of the excretory duct is 

 lost before it ascends to terminate under the lunate head. When thus 

 replete with food, a specimen of the Alcyonella, which forms the encir- 

 cling stratum of a twig, with the hydrse stretching from the surface, 

 seems entirely beset with thorns. 



I must anticipate future opportunities of acquiring sufficient acquaint- 

 ance with the actual structure of the different Alcyonellse ; much is to 

 be still explained. 



AVhere investing a twig, the general aspect of its cellular conforma- 

 tion seems to resemble that of the Lobularia, investing the dark tube of the 

 Amphitrite. It appeared to me that when the animals were in retreat, the 



