ZOOLOGY AND BOTANY, MICROSCOPY, ETC. S91 



granules of various sizes, whicli are quite irregularly arranged. This darken- 

 ing increases, and the granules approximate to one another, and the whole 

 appearance gradually acquires greater homogeneity ; in the homogeneous 

 figures fine achromatic bands appear, which become more and more dis- 

 tinct ; the achromatic substance becomes spindle-shaped, and the chromatin- 

 spheres become collected at the equator ; here they form a true equatorial 

 plate. It is important to note, in connection with the idea that the nuclear 

 snbsfance arises spontaneously, that distinct chromatin-spheres may appear 

 outside but close to an already formed spindle ; these are certainly 

 remnants from the ground-mass of the chromatic substance, and they may 

 finally become connected with some of the granular groups. The author 

 developes in detail the evidence in favour of free cell-formation. 



With regard to the position of the nuclear rudiments in the egg it is 

 important to note that they appear throughout the yolk-masses ; in the 

 early stages there are no indications whatsoever of fission. It cannot yet be 

 decided whether or no the appearance of several protocytes is due to a 

 larger number of spermatozoa entering the germinal vesicle. As soon as 

 formed, but for a short time only, the protocytes increase by indirect nuclear 

 division ; in eggs of the fourth day they are numerous. From their 

 divisions there finally results a nucleus with distinct limits which stains 

 intensely with carmine and hEematoxylin, and has no further internal 

 structure than clear vacuolar spaces. The surrounding plasma becomes 

 much more distinct, and stains (with eosin-haematoxylin) red, while the 

 nucleus becomes blue. 



Before the indirect divisions of the yolk-cells in the interior of the egg 

 cease, the future ectoderm begins to be formed. The superficial cells take 

 a perpendicular or oblique position in relation to the periphery of the egg ; 

 these cells divide, and while one of the two new nuclei becomes again the 

 nucleus of a yolk-cell, the outer one more and more approaches the margin 

 of the egg, and with its surrounding plasma becomes converted into a 

 blastoderm-cell. Dr. Henking ascribes the difiierence in form of the outer 

 and inner cells to the fact that the outer ones have a proportionately smaller 

 opportunity of obtaining nourishment, and an increased supply of oxygen. 

 The blastoderm-cells increase by division in the direction of the periphery 

 of the egg. As so often happens in the development of the Arthropoda the 

 blastoderm-cells wander to one side of the egg, and there divide with especial 

 activity. The history of this stage is entered into with great detail. 



The yolk is next described ; in addition to a large number of small, 

 homogeneous, highly refractive spheres there was a considerable number of 

 larger spheres ; others, intermediate in size, were less common. The larger 

 spheres were not ordinarily homogeneous, but contained one granular 

 nucleiform ball or homogeneous, rounded, or semilunar masses of higher 

 refractive power ; or the spheres were finely granulated, or contained a 

 number of not quite round homogeneous corpuscles. The spheres appear 

 to contain a fluid which is limited externally by a membrane. In addition 

 to the formed yolk-elements there is also unformed paraplastic substance 

 which aids in forming the fluid in which the yolk-spheres are suspended. 

 The author gives a most detailed account of the yolk, many of the charac- 

 ters of which have been already observed in the ova of other Arthropods. 



Dr. Henking proceeds to discuss the changes in the cell-nucleus, its 

 disappearance, and " free nuclear and cell-division " in the various classes 

 of the animal kingdom. He concludes that in all classes a temporary 

 disappearance of the germinal vesicle has been observed, and suggests 

 that first the chromatic substance is broken up, and that afterwards the 

 whole vesicle becomes invisible. Observations on plants as well as 



