the final development of a new individual, which may be accom- 

 plished in other animals by a single copulation." From the same 

 source we learn that Chrysemys (Emys) picta does not lay its egga 

 before the eleventh year. Our other turtles probably lay their 

 eggs from the eleventh to the fourteenth year, according to the 

 species. The operation takes place in the month of June, both at 



effect upon this particular function. 



Before segmentation of the yolk the nucleus, or germinal vesicle, 

 undergoes self-division. According to Agassiz and Clark kt this 

 takes place, at least to a certain extent, without the influence of 

 fecundation within a year, but at the same time has been seen only 

 in those eggs which have been expelled from the ovary. Finally 

 they become the original cells, " the primitive embryonic cells " en- 

 gaged in the composition of the different organs of the body. In 

 the bony fishes, according to CEllacher, the germinal vesicle is 

 ejected bodily from the germinal disk, and Foster and Balfour 

 think this fate awaits that of the birds. In insects the germinal 

 vesicle is supposed to undergo self-division and form the nuclei 

 of the cells of the blastoderm. 



The segmentation of the yolk has been fully observed in Glyp- 

 temys (Emys) insculpta. The process of segmentation is not so 

 regular, and there does not seem to be always, in the beginning, 

 a symmetrical halving of the embryonic area, as has been observed 

 among birds ; but in other respects it resembles what takes place 

 within the eggs of the latter animals, and finally results in shap- 

 ing out the embryonic disk." Agassiz and Clark, from whom we 

 have quoted, think, however, that, from certain phenomena ob- 

 served by them, the whole mass of the yolk becomes segmented. 



The formation of the primitive streak, the amnion, allantois, 

 and chorda dorsalis, are much as observed in the chick, and for 

 an account of the early stages of the embryo reptiles, the reader 

 is referred to the chapter on the embryology of birds. The lungs 

 arise as hollow sacs projecting from the sides of the throat ; the 

 liver is a thickening of the same membrane from which the stom- 



connection with the posterior^end of the^ntestine." 



By the time that the heart has become three-chambered, the 

 vertebrae have reached the root of the tail, the eyes have be- 

 come entirely enclosed in complete orbits, and the allantois begins 



