REPRODUCTION 



171 



one side of the geramule (above in the figure), which is plugged shut 

 during the resting stage. This plug is removed by the developing sponge, 

 which then creeps out. It is greatly distorted while crawling out, for the 

 aperture may be so small as to permit the sponge to pass only several cells 

 abreast. Once out, however, it quickly takes on the form of a sponge 



Fig. 140. — Diagram of bryozoan with statoblasts (s) ; also photograph of animals and (at 



right) a statoblast. 



(Fig. 139, right). Gemmules allow sponges to live through winter and 

 permit them to be carried to other bodies of water. 



In the Bryozoa, or moss animals, the internal buds are called stato- 

 blasts. They appear at first as white or yellow spots along a stalk which 

 joins the stomach of the animal to its body wall (Fig. 140). The oldest 

 statoblasts are next to the stomach. In forming them a mass of cells 



Fig. 141. — Statoblasts of several Bryozoa: a and b, two views of that of Cristatella; 

 c, Pectinatella; d, Lophopus; e and/, floating and sessile types, respectively, of Plumatella; 

 g, J'redericella. (a and b from Sedgwick after Allen; c-g, from Ward's Natural Science 

 Bidletin.) 



comes to be enclosed in a horny cover consisting of two valves, like two 

 cymbals pressed together (Fig. 141a, b); or they may be of other shapes 

 (e-g). These statoblasts escape by the degeneration of the body or 

 some part of it. Some possess floats so that currents of water carry 

 them, and some have hooks which tend to hold them fast to fixed objects. 

 Some germinate late in the summer of the year in which they are pro- 

 duced; others remain undeveloped over winter. They endure long 



