188 MR. NEWPORT ON THE IMPREGNATION OF 



egg in a direction transverse to the first cleavage, may also be advanced as conform- 

 able to the same view. It is further supported by the fact which I have seen in the 

 egg both of the Frog and Newts, that before the second or crucial cleavage is com- 

 menced the yelk becomes contracted, so that the first cleft for a time is almost imper- 

 ceptible while it is extended in the transverse direction, or line of axis of the first 

 division, after which the second or crucial cleft is commenced. To this I may add 

 another fact which appears to be equally significant, and which occurs in the unim- 

 pregnated eggs both of the Frog and Newts, but more especially in the latter. 

 Although no recedence of the yelk from the vitelline membrane takes place in the 

 unimpregnated egg of the Frog, it becomes, nevertheless, slightly oval after the first 

 few hours, but returns to its original shape some time afterwards. But the unim- 

 pregnated egg* of the Newts is not only separated from the vitelline membrane, but 

 also is depressed, and has a distinct pit in the centre of its upper surface, and also 

 assumes an obtuse oval form, both which it retains, when the egg is preserved in 

 water, until decomposition has commenced. 



Changes in the impregnated and unimpregnated Ovum compared. Having traced 

 the egg impregnated by natural union of the sexes through its first period of deve- 

 lopment, I was able to compare the phases it exhibits with those of the artificially 

 impregnated, and these with the appearances in unimpregnated eggs of the same 

 brood, placed under precisely similar circumstances with reference to light, heat, air, 

 water, and locality. The ova experimented on were all procured from the same 

 female, and the seminal fluid from the male with which she was paired, and at the 

 time the female was about to spawn. 



SPALLANZANI obtained unimpregnated eggs of the Frog for his experiments by open- 

 ing the body of the female and removing them from the distended oviducts. This 

 mode is exposed to the objection, that in the removal of the ova they are liable to be 

 brought into contact with the blood of the animal from the cut vessels, and that the 

 ova thus obtained may not be the most mature, and fitted for experiment, it seemed 

 desirable, therefore, to obtain them by another mode, the total withdrawal of the 

 influence of sensation, and power of tension in the muscles by division of the spinal 

 cord through the medulla oblongata. The attempt was made with a female frog 

 that had been paired for several days, and, from appearances, would have deposited 

 her ova naturally in the course of a few hours. The spinal cord was divided as 

 quickly as possible with a strong pair of scissors immediately behind the brain, and 

 this organ was also destroyed, so that all consciousness was annihilated. The attempt 

 was successful. The muscles deprived of voluntary power instantly became relaxed 

 and allowed of the ova being passed, by gentle compression of the body, through the 

 natural passage without contact with the blood of the animal, in greater or smaller 

 number at pleasure, and thus afforded easy means of experiment. 



I may once for all state that it was in this way that the ova were always obtained 

 in the following investigations. 



* Or, possibly, partially impregnated. 



