THE ZOOLOGICAL STATION AT NAPLES. 287 



spireme stage up to the formation of the definitive chromosomes will now 

 be briefly described. As the egg grows, the chromatin undergoes a 

 progressive change both in structure and in staining property. In the 

 spireme stage it consists of a thick filament loosely coiled and lying in a 

 vacuole in the cytoplasm. This filament has a square or polygonal cross- 

 section and is monilated. I did not observe any signs of a longitudinal 

 division of this primitive spireme. Threads (1 linin) extend in ladder 

 fashion between the monilations on adjacent portions of the filament and 

 similar threads (green with nigrosin-light green) moor the coil to the 

 walls of the vacuole in which it lies. Later a definite nuclear membrane 

 lines the walls of this vacuole, and would thus appear to be of cytoplasmic 

 origin. The chromatin of the spireme has a compact appearance even 

 under a ^V oil-immersion lens. 



The chromatin of the spireme stains deep black with iron-haematoxylin, 

 and intensely blue with Delafield's hsematoxylin. During the growth of 

 the oocyte the spireme is gradually resolved into a network in a manner 

 not very clearly understood. The compact substance of the spireme is 

 resolved into distinct granules which are distributed along the threads of 

 a now copious reticulum, but are more massed together at certain points. 

 The germinal vesicle of the more advanced eggs has a beautiful open net- 

 work with very large meshes. In this diffuse form the chromatin does not 

 stain readily with hcematoxylin, but rather vnth acid dyes, such as eosin, 

 orange G, and congo red. It possibly corresponds to the oxychromatin of 

 Heidenhain. This progressive change in staining properties on the part 

 of the chromatin during the growth of the egg may, as Rohde (1903) 

 asserts for cells in general, be the expression of a loss of phosphorus on 

 the part of the chromatin granules (JVucIeinkorper). The observation is 

 quite in line with the chemical researches of Zacharias, Rosen, and others, 

 according to whom the nuclei of the meristomatic cells of plants contain 

 more phosphorus than the nuclei of cells which have been growing for 

 some time. 



Again, when the definitive chromosomes are being formed, that part 

 of the chromatin which goes to form these bodies stains intensely with 

 hajmatoxylin, and, in the fresh state, with methyl green. The remainder 

 of the chromatin — the ' residual chromatin ' of authors — is acidophil in 

 its reaction. 



In connection with the important but difficult question as to which of 

 the manifold appearances in fixed and sectioned cells represent organised 

 structures, and which are mere coagulation products, some observations 

 on the yolk spheres of the egg of Tomopteris may be mentioned. 



The yolk spheres, as may be easily demonstrated in the living egg by 

 pressure under the cover-glass, are fluid or viscid drops, and must, of 

 course, be regarded as inert bodies : they are quite homogeneous until 

 attacked by a fixing reagent, such as a drop of Gilson's fluid let under the 

 cover-glass. The yolk spheres then appear — under a low magnification — 

 to have a uniform granular structure. Under a high power (j\, 

 oil immersion) this granular structure resolves itself into a beautiful 

 uniform network, like that of a nucleus in the resting stage, except that 

 the reticulum is quite uniform throughout. There can be little doubt 

 that this reticulum is a pseudo-structure due to the coagulating action of 

 the fixing fluid. In sections the spheres are often to a greater or less 

 extent dissolved, and cease to fill completely the vacuole in the protoplasm 

 which they formerly occupied. This pseudo-reticulum can be easily 



