190 SUMMABY OF CURRENT RESEARCHES RELATING TO 



Eeicbert and Hansen held a different view, regarding as the ovum 

 only a globular mass found in the free end of the cylinder. 



Formation of the Embryonic Layers in the Trout.* — L. F. 

 Henneguy in dealing with the vexed question of the origin of the 

 primary blastodermic layers in Teleostean Fishes, comes to con- 

 clusions resembling those of Gotte. The jfirst trace of the embryo 

 appears as a thickening at one point in the margin of the germinal 

 disk ; it is found from sections that the cellular layer which roofs in 

 the segmentation-cavity, turns inwards towards the yolk at the margin 

 of the disk, and penetrates this cavity ; the corneous layer forms no 

 part of this fold, but ends on the surface of the yolk. At the projec- 

 tion formed by the embryo, the blastoderm is thicker, and the inflected 

 margin extends further into the cavity than elsewhere. At the pyri- 

 form stage of the embryo, when the posterior extremity forms a slight 

 projection on the edge of the disk, the cells are found to present a 

 concentric arrangement around the axis of the embryo, as described 

 by Oellacher ; the blastodermic layers are not distinct at this point, 

 although in front of the caudal bud two are distinguishable in trans- 

 verse sections made across the embryo, commencing at the caudal 

 bud ; the three primitive layers are found in the lateral parts of the 

 embryo and at the caudal end ; in the middle line only two, but below 

 the axial cord (the commencement of the nervous system) is found 

 the chorda dorsalis, formed from the lower part of the axial cord which 

 originates from the primary endoderm at the same time as the meso- 

 derm. In the anterior part of the embryo also, only the two layers 

 are foimd. Longitudinal sections of this stage show the caudal bud 

 to be formed of undifferentiated cells; in front of it, first two and 

 then three layers are met with ; the ectoderm increases in thickness 

 from behind forwards, but suddenly becomes thin at the anterior ex- 

 tremity. The mesoderm, chorda dorsalis, and secondary endoderm 

 only exist towards the middle of the embryo, and in front they 

 become confounded with the primary endoderm. At that point in 

 front of the caudal bud at which the three layers are developed, a 

 peculiar vesicle appears in the secondary endoderm. The nervous 

 axis is developed at the cost of the ectoderm and the corneous layer 

 takes no part in its formation ; from the first, it is clearly separated 

 from the chorda dorsalis ; when the medullary cleft is about to be 

 formed, the central cells exhibit karyokinetic figures and divide ; the 

 daughter-cells separate, leaving between them a space, the future 

 central canal. These cells are very delicate, whence has arisen the 

 erroneous idea that they normally undergo destruction. 



Distinctions between Organisms and Minerals. f — Dr. H. Valin 

 has repeated the interesting experiments of MM. Monnier and Vogt 

 on the artificial production of organic forms.} 



In a flask full of soluble glass were placed fragments of sulphate 

 of iron, ten grains in weight, which immediately began to assume a 



* Comptes Rendus, xcv. (1882) pp. 1297-9. 

 t Amer. Natural., xvii. (1883) pp. 233-4. 

 i See thia Journal, ii. (1882) p. 320. 



