20 BRITISH FOSSIL CORALS. 



tentaculcs these colour-bearing cells arc arranged in small irregular groups, but elsewhere 

 they become more numerous. 



" The internal membrane lines the interseptal loculi, Mhere its presence is rendered 

 evident by its colour ; it is stopped inferiorly by the last sclerenchymatous dissepiments. 

 The mesenteric folds formed by this membrane present a few colour-cells. The folds^ give 

 attachment to the simple " boyaux pelotonnes " which float in the large interseptal loculi 

 along the smaller septa, and which often show themselves on the columella when the 

 mouth is half open and the polype is slightly contracted. Their walls are almost entirely 

 composed of nematocysts of the largest size, and their surface is furnished with large 

 and strong cilia ; they are frequently affected by ])eristaltic movements, and they arc 

 attached to the tentaculiferous disc by strong muscular fibres." 



IV. — Reproduction and Multiplication. 

 Ovular Rejn'odtiction ; Gemmation; Fissi2)arous and Serial Growth; Reproduction. 



The mesenteric folds and the twisted tubular j}i^ocesses, w'hose ends are free in the 

 visceral cavity, appear to be the organs vphich develop the male and female elements. 



It would appear that all corals are not bisexual, but the majority are so. Spermatozoa 

 w-ere asserted to exist in the tubular processes, but their description tallied with that of the 

 thread-processes of nematocysts. Milne-Edwards dispelled this illusion, and the true male 

 elements have been discovered. The presence of ova in the mesenteric folds and in the 

 tubular processes has been noticed and in the latter position by Michelotti andDuchassaing 

 in large compound corals.^ The ova are matured in the folds and processes, and then 

 escape into the visceral cavity, and are expelled through the stomach and mouth. They 

 have some power of active locomotion, and select favorable localities for their resting-place. 

 The young polypes have faint traces of the future sclerenchyma, and grow rapidly when 

 once fixed, provided they are well nourished. 



As growth proceeds, the structure of the wall determines the shape of the corallum ; 

 and its simple or compound character is regulated by the particidar methods of the mid- 

 tiplicatioH of the individual. Some corals are always simple or solitary, others for a 

 considerable period, and some for a very short time. The kind of yemmation or buddiny 

 determines the massive, dendroid, encrusting, &c., natm'e of corals. 



It appears to be very rare for buds to fall from the j)arent corallum and to form inde- 

 pendent individuals. 



By gemmation is meant the development of corallites from the tissues of a parent 

 corallum. A very small patch of the membrane in immediate contact with the scleren- 

 chyma of the parent appears to pucker, and septa are rapidly formed within the enlarge- 

 ment which occurs ; tentaculcs have already appeared, and the small bud proceeds as if it 

 1 Plate II, fig. 2. = Op. cit. 3 Qp. cit. 



