1865.] Hinces on Zoophytes : the History of their Development. 411 



charged, the zooid having fulfilled its functions appears soon to 

 perish. 



This sketch may suffice to give an idea of the plan of structure 

 which characterizes this class of buds. Of course there are many 

 diversities. The colours, the form of the disc, the number of the canals, 

 the shape of the pendant, the number and structure of the tentacles, all 

 these vary, while in some species there are additional organs of 

 sense on the margin. But the plan of structure is constant. 



To describe the several parts of these animated seed-vessels is an 

 easy task, but it requires the pencil of the artist and the pen of the 

 poet to do full justice to their beauty. Let any one who would realize 

 it glance over the plates in Professor E. Forbes's Monograph on the 

 (so-called) " Naked-eyed Medusae." He brought the skill of the artist, 

 and the fancy of the poet to the illustration of their history, and he 

 has well epitomized their characteristics in saying that " they are active 

 in their habits, graceful in their motions, gay in their colouring, deli- 

 cate as the finest membrane, and transparent as the purest crystal." 



Now at first sight, these floating bodies seem to have little in com- 

 mon with the fixed buds which we found discharging a similar func- 

 tion on the side of the Hydra, and within the reproductive capsule of 

 the Campanularian. 



But if we put out of view for the moment the portions of struc- 

 ture which have immediate relation to independent existence, the 

 swimming-bell and its appendages, we shall have as the residuum a 

 body which is essentially identical with these buds. The central 

 pendant of the Medusiform zoid is represented in this condition in 

 Plate ii. fig. 12 — the disc having collapsed, and the remains of it (6) 

 with the tentacles attached, hanging from the base of it. The disguise 

 being thus got rid of, we recognize at once the structure with which 

 we are already familiar — a bud presenting a central cavity (d) en- 

 closed by the two membranes, between which ova are developed. 

 True there is an opening at the extremity (e), but this also is con- 

 nected with the necessities of free existence, the zooid being de- 

 pendent in this stage of its being on supplies from without, and no 

 longer nourished by the commonwealth. Suppress the mouth, and 

 the body which we are examining is identical (essentially) with the 

 sexual bud of the Hydra, of the Clava (Plate i. fig. la), minus the 

 protective envelope (d), and of the Campanularian (Plate ii. 

 fig. M.) 



The accessory and adaptive organs then, which fit the sexual bud 

 in some cases for a term of free existence, constitute the difference 

 between its simpler and more complex forms. The ova- or sperm- 

 bearing body, which is the essential element, is constant and struc- 

 turally identical throughout the Hydroid series. In the case of the 

 Medusiform zooid it exhibits an advance of development, is furnished 

 with a mouth, and becomes a true polypite, a polypite combining the 

 nutritive and reproductive functions. The (so-called) Medusa is a 

 sexual Hydra (male or female), suspended within a contractile bell, 

 which bears it through the water. The vivid tints which it often dis- 

 plays both on the disc and the peduncle, the gracefulness of its forms, 



