110 xMR. NEWPORT ON THE ORGANS OF REPRODUCTION, 



4. Evolution of the Embryo. 



The Jirst period in the evolution of the embryo extends from the deposition of the 

 egg to the gradual bursting of the shell, and exposure of the embryo within it. 



In my observations this period extended from the morning of the 6th of March, a 

 few hours after the eggs had been laid, to the 31st of the same month, a period of 

 twenty-five entire days. The atmosphere of the room in which the eggs remained, 

 varied throughout the whole time only from about 50° to 60° Fahr. It has been 

 already seen that the G^g of lulus contains all the primary parts of the ovum of Verte- 

 brata while still in the ovisac, and that the chief alteration the e^^ undergoes, after 

 it has acquired a size large enough to be recognizable by the naked eye, is simply an 

 increase of its whole bulk. 



I can offer but few observations on the earlier changes in the e.^g after impregna- 

 tion, a subject already deeply investigated in other classes. I noticed, however, that 

 there was considerable alteration in the appearance of the graniform cells of the yelk 

 within the^r^^ day after the e^^ was deposited. They varied much in size towards 

 the end of the day, some of them being much larger than others. The smaller ones 

 were exceedingly numerous, less globular in form, more opake and granular, and 

 adhered together, as if by a tenacious mucus, more firmly than in the unimpreg- 

 nated e^g, but I could not yet observe any trace of the embryo. The shell was still 

 soft and elastic, and the tg^ became shrivelled and dried up if exposed to the air 

 only for a few minutes. On the second day there was still no marked difference in the 

 external appearance, but in the interior the whole yelk had become firmer, and the 

 cells cohered more together, and I thought I could perceive some faint indications of 

 the future embryo, composed entirely of large and small cells. On the third day the 

 Qgg exhibited no further perceptible change ; but on the fourth its contents were di- 

 stinctly less fluid than at any preceding period, and the cells were more globular and 

 larger. This was very distinct both in regard to the larger as well as the smaller 

 cells. The whole of them were more closely aggregated together, and much more 

 distinct beneath the microscope. Up to this period I had not satisfactorily observed 

 the outline of the embryo, but there was now a little granular mass on one side of 

 the shell, which I was inclined to regard as the future being. The exterior of the 

 shell had also become more firm and less elastic. Unfortunately, at this period I was 

 accidentally prevented from continuing my observations, which I was unable to re- 

 sume until the 25th of March, the nineteenth day after the egg was deposited. There 

 was now a complete alteration in its form. It was more obtuse at both ends, and 

 had become much larger. This enlargement of the impregnated e^g, I have constantly 

 observed in the eggs of Melolontha, Meloe and Athalia, in all of which the shell is 

 elastic. At this period the outline of the embryo coiled up within the shell, and 

 nearly filling the whole interior, was very distinct (Plate IV. fig. 2.). On one side 

 there was a clear transparent space extending about halfway across the shell, indicating 



