Bio THE AMERICAN MONTHLY [Oct. 



though characteristic, it is of secondary importance. 



9. In the infundibular region of the embryo are seen 

 distinct folds and pits, which are nearly obliterated in 

 the adult. A pair of protuberances, dorsad of the hypo- 

 -physis, occurs in the younger forms, and is represented 

 in the adult by a single mesal notch. Dorsad of the 

 hypophysis, occurs in the younger forms, and is repre- 

 sented in the adult by a single mesal notch. Dorsad of these 

 a mesal protuberance, lying between two commissures, 

 is much more prominent in the younger specimens before 

 the commissures are formed. The decision upon homol- 

 ogies of these protrusions of the wall with either the 

 albicans of the higher forms or the hypoaria of fishes 

 must be reserved, there are details of difference in both. 



10. In the turtle, all parts connected with vision are 

 well developed. In the youngest embryo the optic 

 recess is clearly traceable to the eye along the optic 

 nerve, as the remains of the originally open vesicle. 

 This remnant becomes more convoluted, the endymal cells 

 giving an almost glandular appearance, in the stages 

 when the carapace begins to develop. In the oldest 

 embryo this appearance is gone, but the numerous cells 

 of the chiasma in the adult may represent this convolu- 

 ted vesicular remnant. 



11. The optic geminum does not lose the form of a 

 thin roofed single vesicle until in the oldest embryo a 

 mesal depression occurs, forming the paired geminums, 

 and at the same time an extensive union across the meson 

 by means of the geminal commissure, and a division of 

 the cells into two layers arise. The late formation of 

 this solid roof of the geminums is interesting in connec- 

 tion with the fact that in birds the roof is a membrane. 



12. In the latest embryo the cerebellum is only just 

 beginning its growth as a great mesel feature, though 

 considerably earlier it is apparent as a lateral organ. 

 In the youngest embryo its appearance is like that of 



