JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATION OF PLATE IV, 



Illustrating Prof. Ed. Van Beuedeu's INIeraoir on the De- 

 velopment of Osseous Fish. 



Fig. 1. — Egg of Gadoid fish, observed at A^illafranca at seven a.m., showing 

 the blastodisc divided into two enucleate spheres — the granular " inter- 

 mediate layer" and the homogeneous " deutoplasmic globe" with 

 eccentric oil-drop. 



Fig. 2. — A similar egg later in the day (eleven o'clock). The blastodisc 

 consists of many large nucleated cells ; the intermediate layer is still 

 granular. 



Fig. 3. — Optical section of a similar egg at a still later hour of the same 

 day (five o'clock). The superficial cells of the blastodisc are hexa- 

 gonal. In the intermediate layer are seen numerous " free-formed " 

 oval nuclei. 



Fig. 4. — Egg from the same mass on the following day, in optical section. 



Fig. 5. — The same egg focusscd, so as to give a surface view of the inter- 

 mediate layer with its free-formed nuclei and the radiating granular 

 striaj around them. 



Fig, 6. — Optical section of a considerably later stage, showing the blasto- 

 disc, subjacent layer of large cells, peripheral welt of the intermediate 

 layer and cells on the floor and on the roof of the segmentation cavity. 



Fig. 7. — A portion of the egg drawn in fig. 4, showing the flattening 

 form of the enveloping cells of the blastodisc, and the complete de- 

 limitation of cells in the intermediate layer together with tlie presence 

 of free oval nuclei. 



Fig. 8. — A portion of the intermediate layer as seen in fig. 5, in order to 

 show the radiating striaj around the nuclei and the presence of 

 nucleoli. 



Fig. 9. — A portion of the view given in fig. G more highly magnified, 

 showing on the one hand the similarity of the cells of the layer sub- 

 jacent to the blastodisc to those of the intermediate layer, from which 

 they are probably derived ; and on the other hand the very different 

 character of the cells of the blastodisc. 



Fig. 10. — A portion of the floor of the segmentation cavity of fig. 6, show- 

 ing the pinching off' of cells. 



