74 CRISTATELLA MUCEDO. 



germination, — the bud being enclosed in the curious but beautiful 

 cyst. We have an analogy to this in the pupa state of some 

 insects, in both cases the animal remaining quiescent through the 

 winter periods. The reproduction through sexual organs, already 

 referred to in sketching the plan of the Polyzoa, has received a 

 large share of attention from the Professor. He says that the testis 

 and ovary are both found within the sac-walls during the months 

 of July and August, and that on the rupture of the testis the 

 spermatozoa float within the perigastric space. They are thread- 

 like bodies in many of the species without any enlargement at 

 either extremity ; and floating about with a sinuous motion, they 

 ■ thus are brought into contact with the ovary. Some of the 

 species, however, have spermatozoa with a thickened extremity. 

 The subsequent development is carried on within the perigastric 

 cavity, and eventually it is perfected as a pyriform polypede, 

 swimming merrily with rapidly vibrating cilia through the parent 

 cavity. How it emerges from the sac is a matter difficult to 

 determine, no orifice for its escape having been yet discovered. 

 The second method of reproduction is by gemmse, or buds, which 

 grow from the endocyst through the exterior surface of the 

 coenoecium. These appear at first as small tubercles on the 

 exterior surface, filled with granular matter. The tubercle 

 lengthens and expands, and is in its next stage covered with a 

 thick outer membrane continuous with the ectocyst of the parent 

 cell, and having an internal fleshy lining continuous with the 

 endocyst. This latter is full of large, nucleated cells, and the two 

 sacs become the ectocyst and endocyst of the future polypede. 

 The structure gradually developes ; the lophophore, retractor, and 

 general muscles are presently formed ; the oesophagus, stomach, 

 and intestine become soon distinguishable ; but all through this 

 development the future polypede derives all its nutriment from 

 the parent colony. In a little while, however, the process of 

 evagination and invagination is completed, the tentacular crown is 

 perfected, and the young animal then supports its own existence 

 from the outer world. The Cristatellidcc produce their gemmae 

 from points on the sides of the previously existing cells ; there is 

 no branch formation, and the colony expands itself upon the 

 surface of the disc, which has been already described, forming 



