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III. — Observations on some part of the Anatomy of ttvo species of 

 Naked-eyed Medusae. By George Busk, Esq., F.L.S., Presi- 

 dent of the Society. 



(Read October 25th, 1848.) 



Indispensable as the use of the microscope must, at the present 

 day, be considered in the study of the minute structure of all organized 

 beings, there are, perhaps, none so obviously the proper subjects of 

 microscopical research, as those constituting the extensive class of 

 the Acalephae or jelly-fishes. The pellucid transparency of the tissues 

 of most of these creatures, and the extreme minuteness also of many 

 of them, absolutely require that the eye should be aided, to enable 

 us to arrive at any satisfactory result in their examination. At the 

 same time the beauty and variety of form and colour presented in 

 this class of animals, their abundance, and the facility with which 

 many species may be procured, would appear to offer the greatest 

 temptation, even to those who employ the microscope merely as an 

 instrument of rational amusement. But to the scientific inquirer, 

 the study of the structure of these creatures presents a highly in- 

 teresting and important field. The still obscure relations of this 

 class with regard to the rest of the invertebrate kingdom, the inte- 

 resting physiological considerations involved in their modes of 

 development, and the favourable conditions afforded by the peculiar 

 delicacy and transparency of their tissues, for the studying, as it were, 

 of the ultimate elements of the animal structure, all would seem to 

 demand, and to be, above all things, likely to reward the closest in- 

 vestigation. Until lately, however, the microscopical study of these 

 animals does not appear to have been much attended to, or at all 

 events, not to have been very successfully pursued. All that is trust- 

 worthy or useful in this respect has been afforded by Milne -Edwards, 

 R. Wagner, Will, Kolliker and our eminent countryman Prof. E. 

 Forbes. To the beautiful monograph on the naked-eyed Medusae by 

 the last-named author, recently published under the auspices of the 

 Ray Society, I would refer you for the fullest information as to the 

 present state of knowledge respecting the animals of which it treats. 

 I will here merely premise, that in that work, the extensive class of 

 pulmograde Medusae is subdivided into two groups, characterized 



