372 



COELENTERATA ANTHOZOA 



the middle, a circlet of tentacles is formed below the constriction, 

 and division takes place. The upper half floats away with the 

 original tentacles and stomodaeum and becomes attached by 

 the base in another place ; the lower half remains behind and 

 develops a new stomodaeum, mesenteric filaments, and sexual 

 organs. In some of the Actiniaria another form of asexual 

 reproduction occurs, known as " Pedal laceration." In the 

 common British Actinoloba, for example, so often kept in 

 aquaria, the pedal disc sometimes spreads on the glass or rock 



upon which the animal 



Fig. 164, — Longitudinal fission of Actinoloba. 

 (After Agassiz and Parker. ) 



rests, in the form of a 

 thin membrane or film 

 of an irregular circular 

 shape, nearly twice the 

 diameter of the column. 

 As the Anemone glides 

 along, the film remains 

 behind and breaks up 

 into a number of hemi- 

 spherical droplets, which 

 in a few days develop 

 the other organs of a 

 A similar method of 



tentacles, a mouth, mesenteries, and 



complete and independent Anemone. 



reproduction has been observed in several species of Sagartia. 



A true process of discontinuous gemmation has also been observed 



in Gonactinia, in Gorynactis, and in Actinoloba. 



In the Madreporaria, Zoanthidea and Antipathidea, the 

 usual method of reproduction to form the colonies is continuous 

 gemmation. The new zooids that are added to the colony as 

 it grows arise as buds, either from the superficial canals of the 

 cceiienchym, or from the base or body-wall of the older zooids. 

 In these cases the young zooids acquire the same number of 

 mesenteries, and the same characters of the stomodaeum as the 

 original parent. Some further particulars of asexual repro- 

 duction in the Madreporaria are given on p. 387. 



The sexual reproduction of a great many species of Zoantharia 

 has now been observed. The eggs are, as a general rule, ripened 

 in batches, and fertilisation is effected before their discharge from 

 the body. In some cases the sexual condition is seasonal. In 

 temperate climates the generative organs ripen in the spring and 



