492 Bibliographical Notices. 



gular piece was originally a cell ; the wall and contents of the original 

 cells are metamorphosed into the sarcode-like substance, whose origin 

 out of cells has not yet been demonstrated ; the cells themselves 

 however are not so fused together as to be inseparable by reagents. 



2. The columnar bodies of the Rhabdoccela and freshwater Den- 

 droccela consist of a peculiar substance distinguished by its difficult 

 solubility in alkalies and its ready disintegration by water and dilute 

 acids. They differ widely from the urticating organs or "Thread cells " 

 of the Acalephse and Polypes. In many kinds they have a peculiar 

 relation to the nervous system, and may be probably regarded as sub- 

 serving the development of the sense of touch. 



3. The green colouring matter of Vortex viridis and Mesostomiun 

 viridatum is identical with the chlorophyll of plants ; so is that of 

 Hydra viridis and Stentor polymorphic. 



4. The nervous system is developed in all families of Rhabdoccela, 

 and consists of two ganglia united by a commissure, or of a double 

 ganglion with the threads proceeding from it. 



5. The organs of sense occur as eyes with or without lenses, and 

 as auditory organs. 



6. The hard parts of the male organ consist of a substance similar 

 to chitin, distinguished from it however by its solubility in boiling 

 solution of caustic potass. 



7. The hard shell of the ova of Rhabdoccela and Bendroccela, of 

 Clepsine, Nephelis, and Hydra viridis, consists of chitin. 



The poiypidom of Sertularidse and Campanularidse consists of 

 chitin. 



8. In a new species of the Nemertidse, Tetrastemma obscurum, 

 living young were observed in the body of the parent, while hitherto 

 the Nemertidee were only known to be oviparous. The development 

 of the young takes place without metamorphosis. 



9. The development of the stylet of Tetrastemma goes on thus — 

 the handle arises separately as the nucleus of a cell ; the style, on the 

 other hand, is taken from the preformed lateral style-sacs (Spitzen- 

 taschen) ; hence it may be concluded that the styles of the lateral 

 sacs are afterwards to be regarded as really styles in reserve. 



10. In the same Nemertid, as well as in Prorhynchus stagnalis, a 

 new freshwater species, there exists a water vascular system whose 

 existence in the Nemertidse was not yet known. 



We had intended to comment at some length upon some of these 

 statements, but our space will allow of only a hasty reference to a few 

 of the more important : — 



1 . The conclusion that the tissues of the Turbellaria are the result 

 of cell-development ; that therefore the law of Schwann prevails here 

 no less than in the rest of the animal kingdom ; and that thence the 

 sarcode of Dujardin (the formless contractile substance of Ecker) has 

 no right to be considered as a special histological element, will, we 

 believe, be fully borne out in other cases. The substance of the 

 Polypes (including Hydra), of the Medusae, of the Sponges, may 

 alwavs, with proper precautions, be shown to be composed of true nu- 

 cleated cells. These cells frequently manifest " protean" contractile 



