ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 25 



from other authors, but the experiments made by Loeb appear to confirm 

 them, indicating as tbey do that epidermic cells may be directly con- 

 verted into connective-tissue cells. 



Myelocytes of Invertebrates.* — M. Joannes Chatin finds that in 

 animals in general those nerve-elements usually called myelocytes really 

 consist of cells with a voluminous nucleus surrounded by a ring of 

 cytoplasm. He has recently studied the myelocytes of Annelids and 

 Gastropods by the method of Nissl, and finds that in both there is a 

 distinct nuclear membrane. Further, in both, the structure of the 

 nucleus is the same as in the " small nerve-cells with little protoplasm," 

 studied by Eamon y Cajal in Vertebrates. When the chromatin becomes 

 localised in the myelocytes of either Annelids or Gastropods, it accumu- 

 lates in little masses at the nodes of the nuclear network, and may then 

 give rise to nucleoli. 



Intra-Vitam Granula-Staining.f — Prof. J. Arnold finds that it is 

 possible with neutral red and methylen-blue to demonstrate the granules 

 in living leucocytes. He has also succeeded with the tongue, web, and 

 mesentery of the living frog, showing that the granule does not consist 

 of pigment particles taken in from outside, but owes its origin to an 

 intracellular process. The arrangement of the granules, and their 

 relation to indubitable structural elements, lead Arnold to greater confi- 

 dence in his previous conclusion that the granules are important normal 

 components of the cytoplasm, probably arising from a modification of 

 plasmosomes. 



"Islands of Lan^erhans " in Pancreas.J — Dr. Vincenzo Diamare 

 discusses the anatomical and morphological value of these components 

 of the Vertebrate pancreas. He agrees with Giannelli in believing that 

 Langerhans' cells constitute permanent elements of the pancreas ; but he 

 does not consider that there is any evidence that they are of importance 

 in modifying the composition of the pancreatic juice ; on the other hand, 

 they probably produce a characteristic internal secretion. He does not, 

 further, agree with Giannelli's latest theory that the cells are merely a 

 rudimentary portion of the pancreas without functional importance, but 

 believes them to be an important constituent of an organ whose functions 

 are very complex. The conditions in reptiles afford no support for 

 Languesse's view that in these animals the endocrinous tissue is pro- 

 duced by an alternate metamorphosis of the esocrinous tissue during the 

 course of life. On the contrary, the endocrinous tissue is as constant an 

 element of the pancreas in reptiles as in other Vertebrates. 



c. General. 



Variation. § — Prof. Adam Sedgwick took for the subject of his presi- 

 dential address to Section D of the British Association, Variation and 

 some phenomena connected with reproduction and sex. He uses the 

 term variation to include all the differences between members of a 

 species — what we should prefer to call simply the observed differences. 



* Comptes Rendus, cxxix. (1899) pp. 554-5. 



t Auat. Anzeig., xvi. (1899) pp. 568-72. \ Tom. cit., pp. 481-7. 



§ Address to the Zoological Section Brit. Assoc, Dover, 1899, 19 pp. 



