CRISTATELLA MUCEDO. 73 



Allman distinctly states that the young Cristatella emerges from 

 between the two discs, and that it may frequently be seen with 

 the separated valves clinging to its sac. I have had several 

 dozen statoblasts in the aquarium during the winter, and the 

 valves in spring separated as described by Allman : I have 

 detected but one that was fractured across the disc, and probably 

 this had been the prey of some hungry larva. 



The ccenoecium of the Polyzoa has two distinct membranes : — 

 the interior or " endocyst," and the exterior or '^' ectocyst." In 

 Cristatella, however, the " ectocyst " is entirely absent, the whole 

 ccenoecium consisting of an " endocyst " only, which presents 

 below the curious foot-like appendage already referred to. Owing 

 to the invaginating properties of the endocyst, this inner mem- 

 brane is highly contractile at its upper extremity, but becomes 

 thinner and less contractile towards the base. The ectocyst, 

 when present, is composed of a tough, brown membrane, and in 

 many of the genera it is additionally strengthened by the 

 adhesion of siliceous and earthy deposits ; this naturally obscures 

 the microscopical investigation of many of the Polyzoa. The 

 anatomy of these investing sacs is fully described by Allman, and 

 one of the most interesting portions of his monograph treats of 

 his histological researches into these portions of Polyzoon life. 

 In the genus Lophopiis the endocyst is composed of irregularly 

 shaped cells, filled with a transparent fluid, and containing nuclei 

 and nucleoli imbedded in the cell-walls : the whole of the interior 

 of the endocyst he has found to be lined with a system of minute 

 canals, and also by a network of fibres, which he has separated 

 from the sac-wall in a continuous layer. 



The production and development of the statoblasts is, how- 

 ever, but one method of reproduction, and is confined to the 

 winter stages of this interesting creature. All the fresh-water 

 Polyzoa, according to Allman, have a sexual and a non-sexual 

 reproduction ; and he considers that three methods are distinctly 

 observable. ist— The sexual, by means of testes and ova 

 discerned by himself in the pericardial cavity. 2nd — The non- 

 sexual, by gemmse ; and 3rd — The non-sexual, by statoblasts 

 already described. As the statoblasts are destitute of germinal 

 properties, he considers them to be only a variation of budding or 



