ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 191 



"In the Teleostean ovum the protoplasm in the vegetative pole 

 increases rapidly in bulk by an assimilation of its inclosed food-material, 

 and is tbus enabled to bud off cells, wbicb, had the distribution of yolk 

 and protoplasm been otherwise, would have been produced by normal 

 segmentation. Thus arises the distinction between primary and secondary 

 segmentation. The separation of animal from vegetative pole in the 

 herring comes with the formation of the third furrow. The archiblast 

 in the herring, together with the cells derived from the parablast, prior 

 to the formation of the segmentation-cavity, give rise to the epiblast. 

 The vegetative pole then gives rise to the primitive hypoblast, which is 

 in turn differentiated into the mesoblast and permanent hypoblast. The 

 primitive hypoblast, as observed in the herring, is precisely homologous 

 with that of Amjphioxus. In both it becomes differentiated into two 

 lateral plates of mesoblast separated by the notochord, and what remains 

 constitutes the permanent hypoblast." 



Segmentation of Teleostean Ova.* — Sig. E. Fusari has studied the 

 segmentation of the ova of Cristiceps argentatus. (1) The first line of 

 division is across the smaller diameter of the germinal area, and slightly 

 eccentric. It is probably transverse to the future embryo. (2) The 

 second is meridional, at right angles to the first ; and the third and 

 fourth lines of segmentation, though irregular, are meridional. (3) Two 

 meridional segmentations are often seen interposed between the first two. 

 The blastoderm from above exhibits eight triangular cells with convex 

 peripheral bases. (4) In the next stage twelve blastomeres are seen 

 like petals round a central region including four. All the elements are 

 united solely by their bases. (5) The blastoderm appears as an ellip- 

 soidal disc of sixteen peripheral blastomeres, covering other sixteen 

 interior elements. Comparing the phenomena with those of sturgeon 

 ova, Fusari collates (1) the internal blastomeres and the micromeres; 

 (2) the external blastomeres and the macromeres ; (3) the free central 

 covered-in space and the segmentation-cavity. (6) The blastoderm 

 becomes a double layer. (7) The peripheral cells share in this less 

 rapidly than the central elements. In successive stages it is seen that 

 certain blastomeres detach themselves from the peripheral zone and join 

 the central disc. At a certain stage the blastoderm consists of an ellip- 

 soidal disc of cells, and of a delicate nucleated plasmodial zone of proto- 

 plasm. As the segmentation goes on, the nuclei of the plasmodium 

 multiply, first by karyokinesis, afterwards by simple constriction. Thus 

 is formed the perivitelline membrane, periblast, or parablast. The 

 blastoderm at the end of segmentation is equivalent to all the epiblast 

 and a portion of the hypoblast in the sturgeon. The perivitelline mem- 

 brane corresponds to the persisting portion of the primitive hypoblast, 

 is a temporary nutritive organ for the blastoderm, and supplies new ele- 

 ments (for blood, &c.) to the embryo. 



Eggs and Larvae of Teleosteans.| — Mr. J. T. Cunningham having 

 previously described and figured the eggs, embryo, and larva? of a large 

 number of Teleosteans, with diagnoses and drawings referring to fifteen 

 species, now gives, in the second portion of his memoir, an account of 

 w r hat is at present known in regard to the eggs and larva? of the several 

 orders, and furnishes a useful summary of scattered data. The third 



* Arch. Ital. Biol., ix. (1887) pp. 22-4. 



f Trans. Roy. Soc. Edin xxxiii. (1887) pp. 97-13G (7 pis.). 



p 2 



