TRANSACTIONS OF THE SECTIONS. W7 



7. It would require a separate dissertation to illustrate th^ 

 mode of increment peculiar to zoophytes in detail, and to de- 

 scribe their extraordinary reproductive properties. 



The stem of the Tubularia indivisa elongates only during 

 the subsistence of the head. This having fallen, it remains 

 stationary. The elements of this important organ, the recep- 

 tacle of food and the source of the progeny, seem dispersed 

 throughout the stem, and it is regenerated from the residue left 

 by sections very near the root. The original cell of the nascent 

 Sertularia polyzonias is accompanied by a diminutive twin in- 

 vested by a common membrane ; and one is always forking off 

 in future increment as the other gains maturity. Sometimes 

 polypi are regenerated in the vacant cells oi.Sertularice, pro- 

 vided the pith be entire ; but the I'eproductive powers succeeded 

 by violence are not displayed as in the Tubularice. 



Wounds and lacerations, inevitably destructive to the larger 

 animals, are suffered with impunity by those allied to the Hydra, 

 and in promoting the evolution of dormant parts denote that 

 the principle is there. In others of the lower tribes, such as 

 those now denominated Anmdosa, it is doubtful whether the 

 elements of the entire animal do not even reside in every seg- 

 ment. The Amphitrite ventilabrum, which attains twelve or 

 fifteen inches in length in the Scottish seas, regenerates either 

 the higher or lower extremity indifferently when mutilated. 

 The author has found also that very small intermediate sec- 

 tions near the extremity of this and other species regenerated 

 the beautiful complicated anterior plume of branchiae, and the 

 posterior glandular parts, perhaps aiding the construction of 

 the tube. While the body remains a fragment, the former is 

 disproportionately large, nor can its singular mechanical pro- 

 perties be exercised when the redintegrated animal is dislodged 

 from its original dwelling. 



However luxuriant a zoophyte may appear in ultimate ma- 

 turity, though consisting of hundreds of naked animals as in 

 the Cristatella and Alcyonium, or of a thousand cells with their 

 polypi as in the Sertularia and Flustra, the origin of all is one 

 only. Perhaps the formation of the cell and the other inani- 

 mate parts undergoes some modification with the age of the 

 product : the animal with which it originates is equally large, if 

 not larger than any of its successors. 



All the products described in this memoir, except the Cris- 

 tatellce, dwell in the sea, from whence their recovery is often 

 as much the consequence of accident as design. Most of the 

 preceding results have been verified only with years of obser- 

 vation. 



