042 SUMMARY OF CURRENT RESEARCHES RELATING TO 



time of the formation of tbo blastodisc. The young Umbra limi is 

 batched on the sixth day. The air bladder appears three days later, 

 behind the pectorals. By the sixteenth day the pigment has become 

 so abundant as to render the larva very dark. Immediately after 

 hatching, the notochord extends into a lohe projecting at the end of the 

 tail. This lobe, which becomes absorbed as growth proceeds, is 

 homologous with the " opisthure " of Chimaera, and of the larval Lcj>i- 

 dostcus. A similar but smaller lobe is present in the young pike ; 

 but no telcostean approaches the Bhomboganoids in this respect, so 

 closely as does Umbra. 



Mode of attachment of the Ovum of Osmerus eperlanus.* — The 

 ovum of the smelt is usually stated to be attached by a short ligament 

 to solid objects. This " ligament " Mr. J. T. Cunningham finds to be, 

 in reality, the outer layer of the zona radiata. The zona is divided 

 into two more or less distinct layers, the internal layer having very 

 numerous fine pores, and the outer having fewer pores. When the 

 egg is laid the external layer breaks over a small area and unrolls in 

 such a way that it remains attached to the egg over a circular area, 

 whilst the rest of it serves as a suspensory membrane. Before being 

 laid the ovum possesses, outside the zona radiata, a delicate structure- 

 less membrane, derived probably from the connective-tissue layer of 

 the follicle. 



Origin of Blood-corpuscles in Teleostean Embryos.! — Herr H. E. 

 Ziegler has continued his researches on the embryology of Teleosteans 

 in an inquiry into the origin of the blood-corpuscles. 



(a) The corpuscles do not arise from cells of the yolk, as has been 

 stated. There are no cells in the yolk ; but large oval nuclei, under- 

 going modifications apparently of a degenerative nature. 



(b) When the blastoderm has grown round more than two-thirds 

 of the egg, and the space between the parietal plates has extended 

 (about the 13th day), a strand of cells may be observed at the side of 

 the foregut, below the splanchnopleure. The strand extends forwards 

 medianly into the undifferentiated mesoderm mass of the head. As 

 the cavity between the parietal plates enlarges, and as the foregut is 

 medianly separated off from the yolk, the bands of cells above referred 

 to, meet medianly and form the endothelium of the heart. 



(c) Before any blood-corpuscles appear in the vessels, the sinus 

 venosus contains a few which seem to originate as follows : The pro- 

 tovertebras are not sharply defined laterally in the region of the sinus 

 venosus, they protrude between somatopleur and ectoderm in such a 

 way that the connection of the cells becomes loose laterally, and 

 amoeboid cells appear to find their way between the splanchnopleure 

 and the yolk, reaching and entering the sinus venosus. 



(d) A mass of cells described by Oellacher becomes modified into 

 the median vein running below the aorta, and into the blood-corpus- 

 cles which fill this vessel. Before this mass becomes connected with 

 the system, a large number of the cells are given off. In the middle 



* Proc. Zool. Soc. Loud., 188G, pp. 292-5 (1 pi.). 

 t Biol. Centralbl., vi. (1886) pp. 284-5. 



