io6 SCIENCE PROGRESS. 



in fresh preparations stained by the EhrHch methyl-blue 

 method, in the form of a plexus of ganglion cells and 

 branchinpf nerve fibres. 



This plexus is in connection with certain branching cells 

 sparsely scattered in the mesogloea, and it seems extremely 

 probable that these in their turn are connected with the 

 ectoderm, although technical difficulties have made it im- 

 possible to prove this point at present. 



In the Hydrozoa and Scyphozoa the endodermic nerve 

 system can only with much greater difficulty be discovered, 

 and it probable that in the majority of these forms it plays 

 a far less important part than it does in the Anthozoa. 



In Klujostoma Hesse figures a marked endodermic 

 nerve sheath on the outer side of the canal of the tentaculo- 

 cyst. This sends short, tag-like processes into the 

 mesogloea in the direction of the outer sense pit. Corres- 

 ponding with this the thickening of the nerve sheath of the 

 outer sense pit sends tag-like processes into the mesogloea. 

 In the mesogloea of the same region numerous small 

 angular cells are to be seen differing in several peculiarities 

 from the cells found in the mesogloea of other regions. 

 The conclusion seems to be irresistible that at this point 

 there is established a communication between the endo- 

 dermic and ectodermic nervous sheaths by way ot these 

 stellate cells, and the arguments by which Hesse seeks to 

 prove that this is not the case are far from being conclusive. 



Apart from this, however, the endodermic nervous 

 system and its connections of the Hydrozoa and Scyphozoa 

 have not yet been satisfactorily investigated and it is to be 

 hoped that before long some one will with the new methods 

 undertake a thorough investio"ation of the structure of the 

 endoderm of these animals. The facts of the Coelenterate 

 nervous system which may now be considered to be esta- 

 blished are these. That a plexus of fibres and cells occurs 

 in both ectoderm and endoderm similar in structure and 

 probably similar in function. In some Coelenterates such 

 as the Scyphozoa, the Ctenophora, many Hydroids, and the 

 Sea-anemones, the ectodermic nervous system is the pre- 

 dominant one as it is in the Coelomata, but in some of the 



