Bibliographical Notices. 383 



4. The nervous system lies imbedded in this mesenchymal layer ; 

 only the [supraoesophageal ganglion and the] superior margin of the 

 infraoesophageal are in contact with the ectodermal epithelium. 

 ^ 5. The central nervous system consists of a circumoesophageal 

 ring, which not only shows a large infraoesophageal but also a supra- 

 oesophageal ganglionic centrum of a certain significance. Both 

 these centra give origin to arm-nerves ; the nerves of the supra- 

 oesophageal are even more important than those of the other 

 ganglion. 



6. The neiTous centra are formed by thin nervous fibres and 

 very small cells, the peripheral nerves by parallel fibres only, be- 

 tween which nuclei of connective tissue or perhaps of nervous ele- 

 ments are to be found. 



7. The arm-nerves are surrounded by and connected with a 

 ganglionic plexus, situated in the supporting tissues of the arm- 

 walls immediately under the ectodermal epithelium, and formed of 

 large multipolar cells and nucleated protoplasmic threads, inter- 

 communicating so as to form a network. No connexion with the 

 neighbouring epithelial cells was discovered ; but still this seems very 

 probable. 



8. The coelomic body-cavity is clothed with a flat-celled epi- 

 thelium . 



9. The genital glands are supported by a membranous fold of the 

 mesenchymatic layer containing irregular cavities in its axis. 



10. The germinal cells are specially differentiated cells of the 

 coelomic epithelium. 



11. In the investigated species (Terebratula vitrea, Terebratulina 

 septentrionalis, Walclliehnia cranium, BhynchoneJla psittacea) the 



sexes are separated. 



12. The muscles are formed of simple parallel fibres of contractile 

 substance, hardly held together by any connective material, and 

 probably attaining the length of the whole muscle. Adhering to the 

 outer surface of these fibres are nuclei, surrounded by a very small 

 quantity of protoplasm. The striated muscles have in every other 

 respect the same structure as the smooth. 



13. The growth of the shells, in thickness as well as in extent, 

 is exclusively the effect of apposition. 



14. Xo lacunary system as described by Hancock is to be found. 

 Probably the reticulum of connective-tissue cells is mistaken by this 



author for a network of canals. 



These results the author believes to confirm to some extent the 

 opinion of the Hertwigs as to the Brachiopods being typical entero- 

 coelic animals. Their muscles are, according to his opinion, " epi- 

 thelial" ©rgans ; their connective tissue, on the contrary, is a 

 mesenchymatic structure playing a very subordinate part; their 

 generative organs are germinal parts of the coelom-epithelium. 



According to the author's opinion, the Brachiopods are closely 

 allied to the Chcetognathi. The great external differences between 

 thc-» animals are all attributed by him to the influence of the shells, 

 and so considered secondary changes, while, on the contrary, the 



