274 MR. NEWPORT ON THE IMPREGNATION OF THE OVUM IN THE AMPHIBIA 



to 65 FAHR., to afford a greater chance of success ; as all my previous experiments 

 had shown that more eggs became fecundated at a moderately elevated, than, under 

 otherwise similar circumstances, at a low temperature. The instant the object-glass 

 (the half-inch of Ross's microscope) was brought into focus, a vast quantity of sperma- 

 tozoa were seen adhering to the surface of the egg at the part to which the pin's head 

 had been applied. Many of them, attached laterally to the surface, had already 

 ceased to move ; others, only partially attached by their larger end, still vibrated the 

 caudal or ciliated extremity rapidly, but did not appear to penetrate ; while others, 

 more centripetally attached by their body portion, vibrated the free extremity rapidly, 

 and were seen in the act of gradually penetrating into the substance of the envelopes. 

 I distinctly recognised one of these bodies which had just entered the envelope to a 

 depth equal to about twice its own length, and when first seen had not reached so 

 far as the middle or granulous layer of the envelope. Its motion was then slightly 

 serpentine, and its course from without inwards was in a perfectly centripetal direc- 

 tion, with its thicker or body portion extended forwards, and in a line with the 

 centre of the yelk, its progress inwards, as seen beneath the microscope, being as 

 continued and as direct as that of an arrow. I kept this object in focus for several 

 seconds, and watched it through the granulous layer, but ultimately lost it in the 

 more dense and, as yet, unexpanded portions of the inner layers of the envelope, 

 after it had been distinctly seen by a friend, who was with me at the time of the ob- 

 servation. A few seconds afterwards, as the envelopes became more expanded, very 

 many of these spermatic bodies were seen to have already arrived at, and be in the 

 act of passing through the inner or laminated portion of the envelopes, the portion 

 which, when the envelopes have acquired their full distension, by the imbibition of 

 water, is seen to be that which immediately covers the vitellary membrane. A few 

 seconds later a great abundance of them were seen in contact with the vitellary 

 membrane itself; and some were even partially imbedded by their thicker extremity 

 in its substance, and some of these showed an appearance as if they were actually 

 penetrating through it. But in no one instance could I then satisfy myself that they 

 did really pass through ; since by alternately elevating and depressing the lens, and 

 carefully noticing when the margin of the vitellary membrane was most distinctly 

 defined, the appearances of perforation which some of them showed, seemed to be 

 due to the spermatic bodies being imbedded in the membrane at some inclination to 

 the plane of observation and to that of their direction being not quite centripetal. 

 Yet there were other circumstances which seemed to show a likelihood that some 

 spermatozoa do actually pass through the membrane. Thus, within the first few 

 minutes after the impregnating fluid had been supplied to the egg under observation, 

 and at the time when the spermatozoa, which had penetrated its envelopes, were first 

 seen to have arrived at, and begun to enter the laminated portion, or zona pellucida, 

 some of them were noticed to pass gradually onwards for a time, and then suddenly 

 to disappear in an instant ; as if, having passed into this tissue, they had also escaped 



