2 ACCOUNT OF THEIR STRUCTURE. 



by far the most prolific in results ; the voyages which I had the pleasure of making with my 

 friend Mr. M'Andrew around the British coasts having afforded admirable opportunities for 

 the study of our Medusae. These creatures are of so very dehcate and often unpreservable 

 a nature, that casual circumstances usually determined the extent to which the examination of 

 their structure and habits could be pursued, and as most of my observations had necessarily 

 to be made at sea, those circumstances were not always most favorable. In the present 

 very unsatisfactory state of this branch of zoology, however, I do not think it necessary to 

 apologise for unavoidable imperfections, for having often experienced the difficulty of con- 

 ducting inquiries into tribes of which the species had as yet been but vaguely defined and 

 rarely figured, I trust this account of an important and beautiful tribe of animals, of which so 

 far as the British seas are concerned, only a few very fragmentary notices are accessible, may 

 serve as a basis for future and more extensive researches. They offer a fresh and but little 

 explored field for discovery. Their organization is but partially understood, and much requires 

 to be done before the signification of their several parts be fully made out ; of their habits 

 we possess but very slight knowledge. Their development is a subject of the greatest interest, 

 seeing that upon its clearing up will probably depend the future classification of the zoophytes. 

 On most of these points I can scarcely pretend to speak ; what I offer are the rudiments only 

 of an extensive subject. It is for naturalists expert in physiological and anatomical investi- 

 gations, skilled in the use of the microscope, and not too trustful in its revelations, free in 

 their movements, and with time untrammelled at their disposal, to carry out this most interesting 

 branch of research, to which, if my imperfect monograph give an impetus, I am content — 



Quod potui, feci ; quod restat suppleat alter 

 Doctior, et nostris faveat non invidus ausis. 



Before commencing a detached description of the species, it is best to examine the 

 features of organization common to the tribe. 



The parts presented by these animals are the following : 



A. The disk or umbrella. This forms the greater portion of the animal's body. It is 

 hemispheric, but varies from being extremely depressed and almost plane, as in certain species 

 of Thaumantias and ^quorea, to a nearly cylindrical form, as in Turris. One of its commonest 

 shapes is that of a round glass shade, such as is placed over ornaments or statuettes to 

 protect them from dust. It is usually smooth, rarely pilose. Its under surface, on which in 

 certain tribes the reproductive bodies are placed, is called the sub-umbrella. Around its 

 margin internally there is in many species a projecting ledge of membrane called the veil 

 {velum). The margin itself is usually provided with more or less numerous tentacles {cirri 

 marginales), of variable structure, the bases of which are often swollen into a bulb, and 

 deeply coloured or marked with a briUiant spot {ocellus). In the substance of the disk are 

 the vessels, often conspicuously visible. 



B. From the centre of the sub-umbrella hangs a more or less produced proboscis-like 

 body {pedunculus), of variable form and dimensions. In this is the stomach, and, in certain 

 genera, the ovaries. At its extremity is the mouth, surrounded by variously-formed contractile 

 lips, occasionally furnished with produced tentacula. 



Such are the characters visible at a glance. A more minute examination makes us 

 acquainted with the structures they include. 



