192 SUMMARY OF CURRENT RESEARCHES RELATING TO 



portion of tho memoir raises two questions in regard to tho maturation 

 and fertilization of the ovum, viz. (1) Is it possible to trace the trans- 

 formations of the nucleus which accompany the expulsion of tho polar 

 bodies ? and (2) Is there any foundation for Hoffmann's statement that the 

 first segmentation spindle is directed radially, and divides into a super- 

 ficial nucleus which belongs to the archiblast, and a deeper one which 

 belongs to tho periblast. In regard to the first question, Mr. Cunning- 

 ham observed in the ova of Pleuronectes cynoglossus the expulsion of a 

 polar body, and what might be hints of a second, but no nuclear spindle. 

 In regard to the second question, the author suggests that Hoffmann has 

 been misled by tho relative positions in which the two segmentation 

 nuclei are seen when the ovum is in a certain position (illustrated in a 

 diagram) with respect to the axis of the Microscope. 



Origin of Blood in Teleostei.* — Dr. H. E. Ziegler adds another 

 research to the number which have been lately devoted to the origin of 

 the blood-corpuscles in bony fishes. It has been shown by various 

 observers that tho blood-corpuscles arise not from the yolk, but from 

 mesodermic elements. Herr Ziegler has reinvestigated the subject at 

 Naples. 



I. The periblast and the germinal layers. In the Teleostei at the 

 time when the blood-corpuscles arise, there are in the yolk no defined 

 cells, but only " free " nuclei. Morphologically, these nuclei correspond 

 to the nuclei of the yolk-cells in Amphibia. Physiologically, they 

 undergo peculiar modifications associated with the absorption of the yolk. 



II. Tlie origin of the heart. The embryonic heart is a bag with two 

 layers — the pericardial epithelium and the endothelium. The latter, 

 along with a number of wandering cells, arises from a group of meso- 

 dermic cells. The latter are continuous with the mesoderm of the head 

 before the closure of the fore-gut, and are to be seen on each side between 

 endoderm and pericardium (side-plates). When the fore-gut is complete 

 they lie medianly in the interspace between the median portions of the 

 pericardial plates, and laterally under the inferior pericardial plate. 

 They give origin partly to the endothelium of the heart, and partly to 

 the wandering cells. 



III. Tlie embryonic circulation, and IV. The origin of the vessels on the 

 yolk-sac, are then discussed. None of Ziegler's results lend countenance 

 to the origin of blood-corpuscles from the yolk. 



V. The origin of the blood-corpuscles. It cannot be satisfactorily 

 maintained that blood-corpuscles arise from the periblast elements. The 

 wandering cells and the blood-corpuscles are of mesodermic origin. In 

 many Teleostei the principal veins (median united cardinals) arise as 

 solid cellular masses as in the chick. The cells within the vessels form 

 the first blood-corpuscles. In some Teleostei the same process may 

 be seen also in a portion of the aorta. 



Ova of Bdellostoma.t — Mr. J. T. Cunningham briefly describes 

 (a) the ovarian eggs of Bdellostoma, and notes the polar projections 

 which, as in Myxine, are due to thread-like processes of the vitelline 

 membrane ; (b) the sexual organs, with the anterior part containing minute 

 ova, while the posterior part was evidently testicular tissue. In one or 

 two other specimens the whole organ seemed to be testicular. As in 



* Arch. f. Mikr. Anat., xxx. (1887) pp. 596-665 (3 pis.), 

 t Trans. Roy. Soc. Edin., xxxiii. (1887) pp. 217-50. 



