298 Royal Society :— 



stinp;iiished — one ovato, with the invngiimtocl tulx' oeciipving the 

 axis ; tlio other fusiform, with the inviiij^iiiated tube oblique. 



The deeper zone of the ectoderm consists of a very remarkable 

 tissue, composed of peculiar membraneless cells, each of which is 

 ])roloni:;ed into a tail-like process, so that the cells assume a clavi- 

 fonn shape. In most situations, where this tissue is developed, 

 (he processes from several such cells unite \\ith one another, so as 

 to form branching, somewhat botrvllilorm groups, whose common 

 stalk can be followed into Ihe ilbrillated layer. The author is 

 thus enabled so far to conlirm the obser\ations of Kleinenberg on 

 cells of apparently the same significance in J/ifdni. ]n Mi/rio(/iela, 

 however, these cells do not, as in J/i/tfni, reach the surface. With 

 the exception, apparently, of their condition in the transitory arms 

 of the Adinula or locomoti\e embryo, they form cAerywhere a deep 

 zone interposed between the muscular layer and the superficial 

 layer of the ectoderm. This zone is designated by the author as 

 the zone of cluvifonn tissue. Though it is in intimate association 

 with the Ilbrillated layer, the author did not succeed in tracing a 

 direct continuity of the individual librilla) with the processes of 

 the cells (as described by Kleinenberg in I/i/dra). 



The author adopts, as a pi'obable hyj)othesis, the views of 

 Kleinenberg respecting the caudate cells of Hydra, which he 

 regards as representing a nervous system. AVliile the deep layer of 

 ectodermal cells in j[Jj/noihela Mould thus constitute a nervous 

 layer, the superficial layer would represent an epidermis ; and 

 since recent researches justify us in regarding the ectoderm and 

 endoderm of the Ca>lenterata as respectively representing in a 

 permanent condition the upper and lower leaf of the blastoderm 

 in the development of the higher animals, we should thus find 

 Myriothela offering no exception to the general law, which derives 

 both epidermic and nervous tissues from the upper leaf of the 

 blastoderm. 



Qlie structure of the tentacles is in the highest degree interesting. 

 In their narrow stalk-like portion, the condition of the endoderm 

 departs widely from that of this tissue in the tentacles of other 

 marine hydroids ; for it presents no trace of the septate disposition 

 so well marked in these. It is, on the contrary, composed of a 

 layer of small cells loaded \\\i\\ opaque granules and surrounding 

 a continuous wide axile cavity. 



It is, however, in the terminal capitulum of tho tentacle that 

 the structure of these organs departs most widely from any thing 

 that has as yet been recognized in the tentacles of other hydroids. 

 Here a very peculiar tissue is developed between the muscular 

 layer and the proper ectoderm, Mbere it takes the place of the 

 zone of claviform tissue. It forms a thick hemispherical cap over 

 the muscular lamella and endoderm of the tentacle, and is composed 

 of closely applied exceedingly slender prisms, with their iinier ends 

 resting on the muscular lamella, to which the prisms are perpen- 

 tlicular, the whole structure forcibly suggesting the rod-like tissue 

 associated with special sense-apparatus in higher animals. It 



