CRISTATELLA MUCEDO. 75 



three concentric rows studded with polypedes. 



We have to consider, thirdly, the non-sexual reproduction by 

 statoblasts. Those of Cristatella I have already fully described. In 

 the Polyzoa reproduction commences from a swelling first seen on 

 the funiculus, or cord, by which the testis is united to the stomach, 

 and to the endocyst at the bottom of the sac. This swelling 

 increases, becomes oval, and is filled with granular matter, which 

 soon developes into minute cells. An external covering is then 

 apparent, also cellular ; and very soon the interior cell and the 

 newly-formed ring, or annulus, around it becomes too opaque to 

 observe the changes subsequently wrought. The interior cell 

 becomes of a dark brown, and the annulus of a yellow colour ; 

 while the latter is seen to be composed of large hexagonal cells, 

 filled with air. After a time the perfected statoblast separates 

 itself from the funiculus, and falls into the perigastric space, 

 where it remains until the breaking-up of the coenoecium sets it 

 free. The large cells of the annulus being filled with air, allow it 

 then to float among the submerged plants, or to swim freely upon 

 the surface of the water. 



Still another method of reproduction occurs, which Professor 

 Allman treats of under the head of gemmation. \x\ this case 

 masses of buds are developed, and a division at certain points 

 occurs in the whole colony. A constriction may be observed in 

 the coenoecium, which gradually extends until the colony is divided 

 into two portions, and these move away in opposite directions. The 

 sexual and non-sexual reproduction of the Polyzoa has brought 

 this class within the law of "Alternation of generations," and as 

 Professor Allman's excellent work on the " Fresh-water Polyzoa " 

 is not easily accessible, and as his descriptions cannot well be 

 condensed, I quote from it verbatim : — 



" We have, first, as the immediate result of the development 

 of the ovum, a ciliated, sac-like embryo, resembUng in form and 

 habit an infusorial animalcule. It is a non-sexual zooid. From 

 this is produced subsequently, by a process of gemmation, ano- 

 ther form of zooid, namely — the polypede, with a much more 

 highly-differentiated structure, in which the organs of digestion 

 especially hold a dominant position, and which we may regard as 

 sexual or non-sexual, according to the view we take of the relation 



