396 Miscellaneous. 



After the formation of these first muscular cords, the form of the 

 young larvae, which was hitherto oval, becomes slightly modified ; 

 the body becomes more contractile, and soon elongates and shortens 

 itself to a great extent by expanding or contracting in the middle. 

 From the flattened buccal extremity, and on points corresponding 

 with the spaces between the first muscular bands, rounded tubercles, 

 representing the first tentacles, are soon seen to spring. 



The initial number of the tentacles is of course in relation with 

 that of the first vertical muscular bands, or rather of the mesenteroid 

 plates which are inserted upon these. But these plates are not all 

 developed at the same time ; two of them, opposite to each other, 

 first make their appearance ; these grow from above downwards and 

 present at their margin a little knotted band {cordon pelotonne), 

 before the others begin to appear. If we consider that these two 

 mesenteroid plates correspond with the two commissures of the 

 mouth, and that the latter is produced transversely from the com- 

 mencement, before the formation of any lamellar or appendicular 

 organ, we shall arrive at this consequence, that the polype actually 

 presents the character of bilaterality before acquiring the radiate 

 arrangement, and that the former of these types, whilst combining 

 with the other, still continues very apparent for a long time. The 

 examination of the adult Corals shows that it never completely 

 disappears. 



In proportion as the tentacles increase in size and number, trans- 

 verse muscular fibres begin to surround the body,and these rings, which 

 at first are very distant, become more and more numerous, especially 

 towards the extremity opposite to the mouth. This extremity soon 

 flattens and acquires an adhesive faculty. The young polype then 

 presents the most essential characters of its parent. Hitherto it has 

 been swimming freely in the water, turning pretty quickly upon its 

 axis, and having its pedal extremity in front. It preserves the cilia 

 with which the surface of its body is covered, even after it is able to 

 attach itself, and when it possesses three circles of tentacles. At this 

 period the young of A. equina present no trace of the marginal 

 vesicles which are to correspond with these three circles on the cir- 

 cumference of the disc of the adult animal. 



I have stated that the initial number of tentacles in Actinia is six, 

 like that of the first longitudinal muscular bands. It may happen, 

 in consequence of accidental abortions, that this number is only five, 

 or perhaps four, or the fortuitous inequality of the first tentacles may 

 deceive the observer as to the number of elements in this first circle ; 

 but the type is normally hexameral. The exception which I have 

 noticed in A. pedunculata, apparently only affects the second circle. 

 I have, in fact, remarked that momentary checks in the development 

 of the different parts of the second circle were not rare, especially in 

 A. equina, but it is generally completed, as well as the third, in con- 

 formity with the laws established by M. Hollar d. The fourth 

 circle, on the contrary, almost always exhibits with much distinctness 

 the mode of evolution ascertained by M. Milne-Edwards and myself 

 for the partitions of Corals ; that is to say, the twenty-four elements 

 of which it is to be composed, do not make their appearance all 



