610 W. B. HARDY. 



characterised by the possession of an exceedingly distinct 

 nucleolus. The smallest of these cells are generally isolated 

 (fig. 6), and each consists of a nucleus surrounded by a deli- 

 cate pellicle of exceedingly finely granular protoplasm. The 

 whole cell may be only 5 /u in diameter. They form the dis- 

 tinctive feature of the ectoderm of the proximal region of the 

 blastostyles, and, by their number, give to it its great thickness* 

 What part they play we shall see later. 



The remaining constituents of the proximal ectoderm as yet 

 unnoticed are its nervous and muscular elements. These I 

 propose to mention very briefly, for they lie to a certain extent 

 outside the limits of the present paper. One of the most 

 striking features of osmic acid preparations, whether sections 

 or teased, are tufts of branching filaments with curious deeply- 

 staining matter disposed on them in irregular patches and 

 granules (fig. 3). In teased preparations these filaments are 

 seen to largely end in a thick plexus between the columnar 

 cells (fig. 3), but some of them also end in the cells which are 

 developing or have developed a nematocyst (fig. 5). Not 

 infrequently a filament may be seen having on its course a mass 

 of granular protoplasm containing a nucleus (fig. 2). Traced 

 downwards these filaments appear to be connected with a 

 deeply-placed nerve network,^ which in turn is in close relation 

 to the muscle-fibres which are placed immediately upon the 

 supporting lamella. 



If the ectoderm of the gonophore-bearing region of a speci- 

 men killed in the autumn be examined, it will be found to 

 consist of externally a cuticle with columnar cells underlying 

 it, and then an indefinite number of ganglion-cells and cells 



1 Fig. 5 is an accurate drawing made with the aid of a camera lucida 

 of a portion of this nerve complex, which by good fortune was isolated 

 in a teased osmic acid preparation. It exhibits a remarkable fact in the 

 arrangement of this primitive nervous system, namely, that some of the ganglion- 

 cells are enclosed in a fine reticulum, formed by the breaking up of filaments 

 derived from the general nerve network. Since this drawing was made the 

 remarkable researches of Golgi, Ramon y Cayal, Kolliker, and others have 

 demonstrated the existence of similar structures in the central nervous system 

 of the higher animals. 



