910 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Prof. Born describes at length the various phenomena exhibited 

 during the readjustment of the material in different positions of tho 

 ovum. In ova in their normal environment, fertilization seems 

 markedly to accelerate the readjustment. In unfertilized ova tho 

 change takes place very much slower. The penetrating sperm appears 

 to effect a change in the consistence of the egg substances, making 

 them more fluid. 



In following the history of tho sperm, Born has shown that while 

 there is no special micropyle, the sperm cannot enter at any place, but 

 only in a region covered with the pigmented cortical layer. It never 

 enters in regions where the white yolk is on the surface, and this is 

 known to be the more compact. 



Born seeks to explain the level and horizontal position of the 

 nuclear spindle in the axis of the normal ovum in reference to the 

 directive influence exercised by the protoplasm on the nucleus. This 

 varies according to the character and distance of the protoplasmic 

 portions, and the horizontal position of the spindle is the only one in 

 which the directive influences would be in equilibrium. This theory 

 is developed in detail in regard to the different divisions of the ovum, 

 both in its normal environment and when fixed. 



The author inclines to explain hereditary transmission not directly 

 in chemical terms, but in reference to the arrangement of minute 

 elements. Now he has shown that though the general protoplasm 

 be literally turned upside down, and moved about to such an extent 

 that almost no particle retains its normal position in relation to 

 adjacent particles, yet the resulting tadpole is normal : the specific 

 transmitting structure must therefore lie in the nucleus which under- 

 goes no visible change in the readjustment brought about by gravity. 

 This agrees with the independent results reached by Boux. Born 

 compares his observations and conclusions throughout with those of 

 Pfluger, 0. Hertwig, Koux, and Kauber, who have lately worked at 

 the same problems. 



Embryology of Torpedo marmorata.* — Prof. J. v. Perenyi finds 

 that the meroblastic ova of Torpedo marmorata are surrounded by 

 a fine structureless vitelline cuticle ; the nuclei which appear beneath 

 the blastoderm in the trophoblast sink downwards and take on the 

 characters of cells ; these partly give rise to the endoderm, and partly 

 form nutrient yolk; the primary blood-cells appear to arise from 

 them. The lower wall of the enteron is not formed, as in Pristiurus, 

 by the first-mentioned cells of the nutrient yolk, but by the constric- 

 tion of the lateral parts of the embryo. The notochord is constricted 

 off from the endoderm in the form of a canal, which appears first at 

 the middle, then at the anterior, and lastly at the posterior region of 

 the embryo. The membrane which invests the chord is formed of 

 cells, and should, therefore, be called membrana propria rather than 

 cuticula chordae. When the termination of the chord undergoes 

 division, its furcate portions grow between the ectodermal and endo- 

 dermal walls of the developing neurentric canal. The tip of the 



* Zool. Anzeig., ix. (1886) pp. 433-6. 



