190 MR. NEWPORT ON THE IMPREGNATION OF 



diately, but subside gradually when the stimulus imparted by impregnation is not 

 supplied. 



The experiments made to ascertain whether the unimpregnated ovum passes 

 through any stage of cleavage, consisted of four sets, placed in four vessels of equal 

 size, containing each about two ounces of water. Ova were passed from the same 

 female as quickly as possible at the same time into each of these vessels. To one of 

 these marked A, a considerable quantity of a mixture of seminal fluid, one part to 

 three parts of water, was immediately added ; to a second, B, only a single drop of 

 this mixture ; while the third and fourth, C and D, contained only water with the 

 unimpregnated ova, and the four vessels were then placed in every other respect 

 under precisely similar conditions. 



A few minutes after the impregnating fluid had been added to A, I examined 

 some of the ova beneath the microscope, and found a vast abundance of spermatozoa 

 adhering to every part of the surface of their gelatinous envelopes. On other ova 

 from the set B, there were also many spermatozoa attached, but in much smaller 

 number than on the ova of set A. 



In Jive hours andjifteen minutes, the temperature of the room during the interval 

 having ranged only from 53 FAHR. to 54 FAHR., segmentation had commenced vigor- 

 ously, and was strongly marked in the whole of set A. But it had not commenced in 

 set B. It did not occur in these until Jive hours and twenty-two minutes, when it 

 began in these also. Thus there were seven minutes' difference in the commence- 

 ment of the changes in these two sets of ova, a circumstance which led to the belief 

 that this difference might have some reference to the relative quantities of the impreg- 

 nating fluid employed, an opinion which I had long before been led to by observa- 

 tions on the impregnation of the common Earwig, Forficula, in which it had appeared 

 to me that deficiency in the quantity of the impregnating fluid is unfavourable to 

 fecundation. 



No segmentation or cleavage of the yelk took place in the sets of ova marked C 

 and D, which, except in becoming a little oval, as already mentioned of unimpreg- 

 nated eggs, remained, in so far as the appearance of the yelk surface was concerned, 

 in the same state as at a few minutes after spawning, and they continued in exactly 

 the same condition at the end of twenty-two hours. This I have since found con- 

 stantly to be the case with unimpregnated ova, whether they happen to be exposed to 

 a high or low temperature of the surrounding medium. The yelk of the impregnated 

 egg gradually acquires a more intense black colour, which strikingly contrasts with 

 the dull colour of the unimpregnated. 



At the end of six days the majority of the ova in A and B were producing embryos, 

 while those in C and D were fast decomposing. 



These trials afforded the positive test I required from direct observation, as a fixed 

 point in the experiments about to be commenced, that segmentation certainly does 

 not take place in the unimpregnated ovum. 



