xlvi INTRODUCTION. 



freshwater Polyzoa. Some of these determinations may 

 be open to criticism, and certainly require the confirma- 

 tion of further research; but on the whole the Firm-h 

 zoologist seems to me to have made good the leading 

 points of his case, and to have worked out with much 

 ingenuity and skill the morphology of this tissue. 



We pass now to the functions of the endosarc. If not 

 a nervous system, what part does it play in the economy 

 of the polyzoon ? 



According to the observations of the writer just quoted, 

 it equals in importance the principal constituent tissues, 

 and deserves to be ranked as one of them. Its relation to 

 the floating corpuscles in the perigastric fluid has already 

 been noticed. It is also the source of the male reproduc- 

 tive elements, and in a large proportion of cases, if not 

 universally, of the ova*. It has long been known that 

 the spermary is developed on the funiculusf- Mother 

 cells, each containing one or more minute nucleated 

 vesicles, are differentiated from the substance of the cord, 

 and cluster thickly round it, forming an irregular massj. 

 They finally detach themselves, singly or in clusters ; and 

 from each of the contained vesicles a spermatozoon is 

 liberated. The spermary is present on the funiculus at 

 a very early stage in the development of the polypide (as 

 I have observed in Farrella repens], and usually occ-upios 



* In this section I shall report in brief the conclusions at which Joliet 

 has arrived, with such critical and illustrative remarks as they may suggest. 



t Allman, indeed, describes the testicle in the freshwater PahtdiceUa as 

 attached to the inner surface of the endocyst ; but it is placed at the point 

 where the funiculus reaches the cell-wall, and no doubt has its origin in it. 



J Smitt has described the production of spermatozoa from the floating 

 corpuscles in the perigastric fluid in the absence of any definite spermary, 

 these corpuscles being, as we have seen, derived from the endosarc (' Om Hafs- 

 bryozoernaB Utveckling och Fettkroppar,' pp. 3J, .T8). 



