Dr. Cobbold on the Anatomy of Actinia. 123 



brane and formation of stomachal cavity, — commencement of 

 tentacula (a), and ovarian septa {b), by the same process of in- 

 volution. These observations on the development are corro- 

 borated by the following remarks of Sir J. G. Dalyell ; speaking 

 of the corpuscula (Rare and Remarkable Animals of Scotland, 

 p. 209), he says, " The motion subsisted eight days, but the 

 shape of some was changing, and elongating prominences were 

 rising on others. Their form improved, when I concluded that 

 they would certainly become Actinia. The rudiments of ten- 

 tacula became visible in the largest in ten days more, and in two 

 days they proved six in number." 



In reference to the behaviour of the young of Actinia imme- 

 diately on their quitting the parent, it was noticed in those 

 under our observation, that they slowly sank to the bottom of 

 the basin, lighting and resting upon their outspread tentacula, 

 with the base or convex portion corresponding to the sucking 

 disk, uppermost ; they then elongated and moved this part of the 

 body laterally, after the manner of Hydra; and if the mother 

 Actinia or any projecting body lay in the vicinity, they imme- 

 diately attached themselves to it and there remained. Some of 

 the young thus adhering to the adult polyp gave the idea of a 

 gemmiferous mode of reproduction, which circumstance may, we 

 think, explain the notion of increase by gemmation, hitherto 

 ascribed to the whole group of these animals, but only actually 

 demonstrated (so far as we are aware) by that careful naturalist 

 Sir J. G. Dalyell, to have taken place in one species, viz. Actinia 

 lacerata*. 



In those species [A. gemmacea) that we exhibited to the Phy- 

 siological Society, the fissiparous mode of propagation was well 

 seen, the serrated line of demarcation indicating that reunion of 

 the halves was effected by a similar process to that which takes 

 place in the cranial bones of the higher animals. An interesting 

 analogy to the phsenomena above described, we are informed by 

 Mr. J. R. Mummery, obtains in the young of Tubularia indivisaf: 

 " Slowly it emerges, withdrawing its tentacles in succession, until 

 it has set itself free, when it crawls slowly upon the bottom of 

 the vessel containing it, elevating itself on the extremity of its 

 tentacles. After a period of time, varying from one to four days, 

 the animal having selected a suitable stone, or the surface of the 

 old poly pidom, reverses its position, and with the mouth upwards, 

 now attaches itself by the opposite extremity and remains rooted 

 fast for hfe." 



* Illustrations of this are given in his work, vol. ii. pi. 4/. 

 t See an excellent paper in the Microscopical Society's Transactions, 

 new series, p. 29. 



