308 W. M. BALDWIN. 



extremity of the embryo is shown above to the left resting upon 

 the trunk of the embryo. Here again approximately the long 

 axis of the brain tube has been encountered by the section knife. 

 Stratification of brain walls has begun. The enteron together 

 with the notochord lie to the right in the sketch. The meso- 

 dermal cells constituting the wall of the pharynx lie immediately 

 ventral to the brain tube. Fig. 16 presents these same general 

 features and, in addition, a bifid appearance of the caudal 

 portion of the neural tube upon the right side of the sketch. 

 The ectoderm folds in between the two tube-halves each of 

 which, while presenting an entire tube, demonstrates its deriva- 

 tion by reason of the thinning of its medial wall. This appear- 

 ance has been previously referred to in the paper on the condition 

 of spina bifida. 



It is to be noted that not one of the histological sections, 

 which are presented, as was mentioned before, as merely typical 

 instances of the appearance of the tissues during the different 

 developmental stages of the embryos, presents any indications 

 whatever either of cell or of tissue disorganization. There is no 

 indication of the presence of degenerated areas of protoplasm 

 either in the yolk mass or in the normal body cavities, nor can 

 there be found any degenerated or extruded nuclei. The organs 

 of the embryo such as the enteron, the brain, the cord, the myo- 

 meres, the notochord, and so on, seems to be normally formed 

 and are of the normal size. So far as can be ascertained through 

 the study of longitudinal sections of the myomeres at the level 

 of the bend in the trunk the cause of this phenomenon is not, 

 apparently, referable either to a degeneration or to a falling 

 out of myomeres upon the concave side of the trunk. As might 

 be reasonably expected, however, the myomeres upon this side 

 have a form which departs from the normal in so far as the 

 segments conform to the concavity. The corresponding seg- 

 ments on the opposite side of the fold are consequently relatively 

 elongated. The normal morphological appearances of the tissues 

 argued for a normal physiological activity as well, and this seemed 

 to be attested by the movements and general vitality of the 

 tadpoles. None of these tadpoles was permitted to live, however, 

 to the period of transformation. 



