INTRODUCTION. 



interesting researches, which have added a new and most 

 important chapter to the history of the Polyzoa. So 

 far, however, as the " colonial nervous system " is con- 

 cerned, we hardly seem to require other evidence than 

 that which has been already adduced. It is indeed, not 

 impossible, as Nitsche allows, that certain of its elements 

 might serve for the transmission of stimuli (a view which 

 has been adopted by Reichert) ; but in the light of the 

 later and more searching investigation we must, it seems 

 to me, admit that as a system it wants the essential 

 characters of nervous tissue. 



ORIGIN AND FUNCTIONS OP THE ENDOSARC. The tissue, 

 commonly known as the " colonial nervous system/' but 

 to which I shall now assign Joliet's name, is, according 

 to this author, a derivative from the endocyst. Tt is 

 formed by differentiation of the cells in the growing ex- 

 tremities of this membrane; these become detached, send 

 out prolongations posteriorly (which ultimately anasto- 

 mose), and constitute the rudiments of the endosarc*. 

 The latter maintains numerous relations with the endo- 

 cyst, but is histologically distinct from it, being com- 

 posed for the most part of fusiform cells, usually (but 

 not universally) destitute of a clearly defined nucleus. 



The endosarcal system comprises the funiculus, the 

 connective cord, and the network so often associated 

 with them, both in the zooecia and in the compartments 

 of the stem, and also (according to Joliet) the paren- 

 chyma in the stem and stolon of Pedicellina, and the 

 muscular layer connected with the endocyst amongst the 



* Joliet states that be has observed this process in many species. It would 

 be satisfactory to have a somewhat fuller account of it than he has giren us. 



