POLYZOA. 



555 



consist of brown pigment masses contained in the zooecia, and are 

 derived from the breaking down of the tentacles, alimentary canal, 

 and nervous system of the polypides. A new set of these organs 

 may be formed from the persistent body-wall of such partially 

 degenerated polypides, as an internal bud. The brown body finally 

 breaks up, and its pigments may pass into the new stomach and so 

 out by the anus. It is this degeneration of the tentacles, digestive 

 organs, etc., and the subsequent acquisition of a new set by growth 

 from the body-wall, which gave rise to the idea that the zooid of a 

 Polyzoan colony really consists of two individuals one the poly- 

 pide, and the other the zooecium or house of the polypide, which 

 has the power of budding new polypides (tentacles, alimentary 

 canal, etc.). 



The funicular tissue contains numerous transparent cells with processes, by 

 means of which they are suspended in the funicular network. They may be 

 faintly yellow in colour, and are regarded as excretory* in function. As there 

 is no organ for the ejection of such excreted matters to the exterior, it is 

 supposed that the disruption of the internal organs resulting in the formation 

 of the brown bodies, and the subsequent ejection of the latter through the 

 alimentary canal of the new polypide, are the means by which excretory products 

 are removed from the colony, t 



Reproduction is partly sexual and partly asexual; in the latter 

 case it may be effected by the so-called statoblasts or by budding. 

 The generative cells are products of the coelomic lining (vide p. 553), 

 -and are dehisced into the coelom. 



The name statoblast (Fig. 444) was given by Allman to certain 

 peculiar reproductive bodies which were formerly regarded as hard- 

 shelled winter eggs, but by him 

 were recognized to be multi- 

 nuclear and of the nature of 

 internal buds. These statoblasts 

 are found only in the Phylacto- 

 laemata : they arise from masses 

 of cells which appear, mainly 

 towards the end of summer, on 

 the funiculus (Fig. 440). They 

 usually possess a lens-like, bicon- 

 vex form, and are enclosed by 



FIG. 444. Statoblasts of Cristatella mucedo 

 (from Allman). a, from the surface b, 

 from the side. 



* S. F. Harmer, " On the Nature of the Excretory Processes of Marine 

 Polyzoa," Q. J. M. S., 33, p. 123. 



t Of. Tunicates, in which there is no apparatus for voiding the excretory 

 concretions which are stored in various parts of the body. 



