402 SUMMAKT OF OUBBENT BESEABCHBS BELATING TO 



omphalo-eephaly, acephaly, heterotaxy, curvature of the spine, &c. 

 Now, the author was able, by varying pressures on different parts of 

 the embryo, to produce such monstrosities, which he describes and 

 figures. 



The older observers considered that the amnion was in some way 

 connected with these teratological phenomena, but M. Warynski, 

 in the course of his experiments, destroyed the amnion, and yet the 

 embryo continued to develope normally. By means of transverse 

 sections through later stages of embryos, in which duality of the heart 

 was suspected, the author was able to study the vascular system : 

 each heart consisted of an auricle, a ventricle, and a bulbus ; the two 

 bulbi unite to form a truncus, which then divides to form the aortic 

 arches. There existed some asymmetry in the venous system. 



The reasons are given at some length for the opinion that the 

 curvature of the body is due to rapidity of the increase of growth ; 

 moreover, the arrest of development of one part of an embryo having 

 a given rapidity of increase, induces an exaggeration of this rapidity 

 in some other part. By pressure on an embryo before any curvatures 

 have made their appearance, he obtained a vermiform embryo, which 

 normally should have exhibited well-marked cranial and dorsal 

 flexures. By injury to the fore-brain a very much greater dorsal 

 flexure was caused, whereas the cranial flexure was absent. In natural 

 conditions the pressure on the embryo is probably caused by the 

 cooling of the egg during incubation; by means of removing a 

 portion of the shell from an incubated egg, and letting the egg cool, 

 the author found that the yolk gradually approaches the shell on 

 the side of the blastoderm, as the cooling goes on, till ultimately 

 the whole blastodermic surface presses close against the shell; in 

 this way the duality of the heart, arising from the cooling of the 

 eg?, is usually accompanied by other teratological effects, since the 

 pressure has occurred over the whole embryo. 



Eggs of Bony Fishes.* — -Herr P. Owsiannikow first describes the 

 egg-capsules of the perch and of the trout ; and in the course of his 

 account he remarks that he has never observed the entrance of leuco- 

 cytes, as described by His and others. The egg-membranes of Lota 

 vulgaris are next described, and then the ovaries of those that have 

 spawned are considered ; the author discusses the eggs of Osmerus 

 eperlamis, and the egg-membranes and yolk of Acerina vulgaris. Gas- 

 terosteus, Coregonus, Esox, and Anguilla fluviatilis are next taken in 

 hand; and then the formation of the ova in the ovaries of Perca 

 fluviatilis. The eggs of the lamprey, their fertilization and early 

 development, form the subject of the concluding part of the essay, 

 which is essentially descriptive, and requires the assistance of the 

 plates to be adequately understood. 



Pelagic Stages of Young Fishes. f — Prof. A. Agassiz describes 

 the pelagic stages of young fishes, which, for the sake of convenience, 

 he divides into (1) those with one or more oil-globules, and (2) those 



* Mem. Acad. Imp. St. Peterabourg, xxxiii. (1885) 54 pp. (3 pis.), 

 t Mem. Mils. Comp. Zool. Cambridge, xiv. (1885) (19 pis.). 



