ZOOLOGY AND BOTANY, MICEOSCOPYj ETC. 929 



into closer proximity at the edge of the fibre. " The sarcolemma is 

 a delusion. It is so firmly established in the conceptions of histologists, 

 that this short essay will hardly avail to displace it. Nevertheless, in 

 time, it will disappear from the text-books." 



Nervous System of Amphioxus.* — Dr. E. Eohde has made a detailed 

 investigation of the histology of the nervous system of Amphioxus, in 

 continuation of his previous researches on that of Chsetopods. The chief 

 interest of the memoir lies, on the one hand, in the completeness of the 

 account, but even more in the critical review of other researches bearing 

 on the histology of the nervous system. It does not admit of summary. 



B. INVERTEBRATA. 



Myelocytes of Invertebrates.j — M. J. Chatin does not agree with 

 the view that myelocytes can be compared to free nuclei. They repre- 

 sent true cells, and possess all the essential parts of these elements. 

 This may be proved with various forms of Invertebrates. These cells 

 are always very small, but they do not vary in size as much as those of 

 Vertebrates (6 /x, to 18 /x), for they are never less than 9 /x nor more than 

 15 /x long. The protoplasmic portion of the element never occupies 

 more than a narrow peripheral zone, and this explains how it is that it 

 has escaped the attention of many observers ; it has often fine granules 

 scattered in its substance. The nucleus, which is always very large and 

 effaces or masks the other parts of the element, is elliptical or spheroidal, 

 rarely polyhedral in form. The nuclear mass is always more granular 

 than the somatic portion of the myelocyte. The nucleoli vary somewhat. 

 The secondary products of the cell are chiefly represented by adipose 

 globules or pigment granulations ; the former are generally placed in 

 regions parallel to the long axis of the nucleus, while the pigments are 

 found near the poles of the myelocyte. 



According to classical descriptions, the myelocyte of Vertebrates 

 has constantly two prolongations placed opposite to one another. Many 

 Invertebrates (such as Pontobdella, Arenicola, Locustd), have only one 

 process, while other (Gastropoda) have several. The prolongations 

 unite to form a fibrillar network, the nature of which becomes mixed 

 when connective fibres take part in its constitution. 



The variations observed in the form of the myelocyte are determined 

 by corresponding variations in the nerve-cells ; when all the myelocytes 

 are unipolar the nerve-cells are unipolar too ; when the former are 

 multipolar the nerve-cells have generally the same form. The author 

 thinks that there can be no doubt that, histologically, the myelocyte is 

 allied to the nerve-cell, and he doubts whether it should be specially 

 distinguished from other forms of nervous cells. 



Anthropotomists have long insisted on the localization of myelocytes 

 in the grey substance or in the retina ; in Invertebrates these cells have 

 a very similar mode of grouping ; they are chiefly observed in ganglia 

 of high physiological value which give off nerves of special sensibility, 

 and they are found near the optic rods. 



Eole of Symbiosis in Luminous Marine Animals. | — M. E. Dubois, 

 who has already urged that the fundamental reaction necessary for the 



* Zool. Beitr. (Schneider), ii. (1888) pp. 169-211 (2 pis.). 



t Comptes Keudus, cvii. (1888) pp. 504-7. J Ibid., pp. 502-4. 



