424 



MOLLUSCOIDEA. 



Tulndipora, verrucosa. 



a. Part of a stock (magnified) ; b, A few cells (highly 



magnified) ; c, A stock (nat. size). 



which may be taken as typical of this suborder, the relation between the infolding 

 portion of each individual and the rigid cell differs from that in the Chilostomata ; 

 and the aperture of the cell is terminal and wide, passing into the soft anterior end 



without narrowing. Tubulipora, is one of 

 the numerous round -mouthed forms, the 

 stocks of which form cup-shaped incrusta- 

 tions, the individuals radiating outwards as 

 seen in the magnified figure (a). In Fig. b, 

 several cells are still more highly magnified. 

 Fig. c shows the natural size of the colony. 

 The moss- animals seem to be excep- 

 tionally rich in methods of reproduction. 

 There is, firstly, the sexual reproduction 

 above mentioned ; secondly, the multiplica- 

 tion of individuals by budding and stock 

 formation ; and, thirdly, a peculiar repro- 

 duction, found in fresh -water forms, in 

 adaptation to external conditions, enabling 

 the animals to tide over the cold of winter, 

 or the drying up of ponds, etc. This last 

 method deserves description. It is effected 

 by means of germinal bodies, which may 

 be of two kinds. In the genus Paludieella, 

 the germs are produced in the course of a few days at the end of September by 

 simple constriction or breaking off of portions of the stock, which then perishes. 

 These detached portions vary greatly in size, and resemble buds of the same size, 

 which latter however remain connected with the stock. They are, in fact, detached 

 buds, called winter-buds, which adhere to the dead remains of the horizontal creeping 

 stem of the Paludieella stock, and the next spring either grow out at the same place 

 into new colonies, or are swept away by the water to form fresh colonies at a 

 distance. The other germinal bodies, termed statoblasts, form as cell-masses on the 

 strand known as the funiculus, which holds the stomach in place, also at the end 

 of September. They are round or oval in shape, and become surrounded by a 

 peculiar horny transparent shell, which is brown or yellow in colour, and consists of 

 two valves fitted one upon the other like watch-glasses. A number of these 

 statoblasts may be seen inside the colony in the illustration on p. 425. The 

 edge running round the two valves is often widened and contains small air-chambers, 

 or else horny filaments which stand out radially and have barbed tips. This ring is 

 termed the swimming-belt, and is a hydrostatic apparatus, which supports these 

 winter-buds or statoblasts on the surface of the water. The complicated barbed 

 hooks apparently act as anchors, by means of which the passively swimming 

 statoblasts catch on at points suitable for their development during the course of the 

 next spring. As soon as the time for development comes, the two valves split apart, 

 and the germinal mass emerges from between them. Here, then, we have an alter- 

 nation of generations. Out of the winter-buds and statoblasts asexually produced 

 individuals arise, which then reproduce themselves sexually, their descendants again 



