308 THE AMERICAN MONTHLY [Oct. 



center of tlie geminum, the union of tlie myel with the 

 oblongata and the tip of tiie olfactory lobe, in the 

 youngest embryo, the figure formed is an isoceles tri- 

 angle, in the succeeding stages changing to a flattened 

 triangle by the elongation of thel)ase. The ce])hMlic limb 

 of the triangle increases greatly, while the folding of the 

 caudal part of the brain produces an actual shorttning 

 of the caudal limb of the triangle In the aduit Amyda 

 the flattening of the triangle has proceeded to an extreme. 

 The change of form in the brain is aj)parently greater 

 between the time when the external appearance of the 

 adult is established, as in the oldest embryo, and the true 

 adult condition, than between the oldest and youngestof 

 the above described embryos. This is due to the fact 

 that after the external adult appearance is complete the 

 cerebrum and the cerebellum both acquire their largest 

 comparative growth. 



2. At the constriction occurring in the brain-tube, 

 between the postcommissure and the floor of the cranial 

 flexure, the brain shows the least increase in size, as shown 

 by diff"erent measurements upon the meson of the embryo 

 and adult brain. This stationary condition is probably 

 due to the early maturing of the region. 



3. The union of the olfactory lobes across the meson 

 was not found in these turtles until the beginning of the 

 carapace was distinguishable, and did not present the 

 comparative extent and close connection of the adult 

 until the oldest embryo had the adult appearance. That 

 is, as was found with the sparrow, the union across the 

 meson is of late occurrence and secondary importance. 



4. Those parts of the cerebrum, apparently connected 

 with olfaction, the hippocampal, progress with equal 

 step with the olfactory lobe, and not until the oldest 

 embryo is the fimbrial edge of the hippocamp and its 

 union across the meson, the fornicommissure, well estab- 

 lished. The late appearance of this commissure is con- 



