202 ME. NEWPORT ON THE IMPREGNATION OP 



dorsales are proceeding rapidly to meet, and form the median dorsal sulcus of the 

 growing body. But the corresponding ova in set I had not been carried further than 

 to the earliest perceptible indications of the area germinativa. 



These facts sufficiently prove the great influence of temperature on the develop- 

 ment of the embryo in its earliest stages, as the comparative numerical results do 

 also its effects on the impregnation of the ovum. Out of eighteen ova placed in 

 the higher and increasing temperature, thirteen produced embryos at nearly similar 

 stages of growth ; while of nineteen ova maintained in a low and diminishing tempe- 

 rature only eight became segmented, and but three of them arrived at the tadpole 

 state. 



A somewhat similar but more marked result took place with the ova of No. 2 in 

 the two sets of experiments. The impregnating means employed in these trials had 

 already been forty minutes mixed with water on the filter. Out of forty-eight ova 

 employed in set H, twenty-five became segmented, and ten of these produced young. 

 But in set I fifty-one ova gave birth to only two embryos. 



In the third experiment of each set the difference is as strongly marked. As the 

 filtered fluid employed in both was the same, and the very few spermatozoa con- 

 tained in it were by the same means brought into contact with the ova in each, it 

 might have been expected that each would have produced embryos. But while the 

 production of a single tadpole in the one case, at a high temperature, may be looked 

 upon as leading to the inference that these bodies are the efficient agents in impreg- 

 nation, the entire absence of all appearance of impregnation in the ova of the other 

 set, to which the same fluid had been equally applied, seems to point to the cause of 

 failure in this case as depending on the prejudicial effect of a low temperature of the 

 surrounding medium on their agency. 



The temperature of the surrounding medium ought, therefore, always to be borne 

 in mind when we are attempting to deduce conclusions from experiment on impreg- 

 nation and development. The presence of light appears to be only of secondary con- 

 sideration as compared with heat ; since in set H, from which light was carefully ex- 

 cluded, not only did impregnation take place more certainly and rapidly than in set I 

 which were exposed to light, but the embryos also were produced in greater number, 

 and acquired maturity in less than one-half the space of time than in the latter ; the 

 only difference of circumstance between the two sets being degree of temperature. 



Influence of Aeration. Next in importance to heat is a free aeration of the ovum. 

 This is of less consequence with reference to impregnation than to the subsequent 

 production of the embryo. In every set of experiments there are always some ova 

 more advanced than others. These are ova which have been nearest to the sur- 

 face of the water, and which, consequently, have been more completely aerated as 

 well as exposed to a slightly higher temperature than others at a greater depth. It 

 is from this cause chiefly that the results of experiments on artificial impregnation, 

 and even of observations on naturally impregnated ova, are always less complete and 



