DEPARTMENT OF EMBRYOLOGY. 77 



embryo, in which the difficulty of distinguishing between real and accidental 

 differences is increased by the varied conditions under which the material 

 for study is obtained. This meant the study of more specimens and better 

 photographic records, planned so as to display clearly the individual regions. 

 Toward this end Professor Spaulding made in this laboratory, in 1921, a 

 detailed study of the steps in the differentiation of the external genitalia. 

 The successful outcome of his investigation testifies to the wisdom of tem- 

 porarily limiting one's attention to a definite region. It is clear that before 

 a satisfactory series of developmental stages, based on external form, can be 

 decided upon, it will be necessary to study each part of the body and estab- 

 lish the normal sequence of differentiation, region by region. 



During the past year I have studied the branchial region in the same way 

 that Spaulding studied the external genitalia and have followed the trans- 

 formation of the tissues in the neighborhood of the first gill-cleft into the 

 definitive auricle. In addition to the detailed information obtained concern- 

 ing the surface anatomy of the embryo, several features in the development 

 of this region have been brought out through this study which are of import- 

 ance because of their bearing upon the more general problems of development. 

 I may mention particularly the evidence of the participation of the ectoderm 

 in the differentiation of the underlying tissues. The study referred to shows 

 that the auricular cartilage acquires its form with all the precision and in- 

 dividuality shown by other cartilaginous parts of the body. The examina- 

 tion of a great many specimens, covering the period from 30 mm. to full term, 

 reveals the fact that there is a great variation in the detailed form of the 

 auricle just as exists in the adult ear; that is, the individuahty of the ear is 

 expressed early, as soon as the respective parts can be identified. The part 

 that varies least is that concerned in the attachment of the ear to the head, 

 while the part varying most is the scapha-helix. An important consideration 

 in the study of the am-icle of the embryo is the functional bearing of its com- 

 ponent parts. In view of this, I examined the auricles from a representative 

 series of adult primates and compared them for the presence of uniform 

 characteristics and the correlation of the latter to the special functional re- 

 quirements of the various species. As in the embryo, the most uniform part 

 is the apparatus for the attachment of the auricle to the head; the next in 

 order is that portion concerned in the conduction of sound-waves into the 

 meatus, together with its protective closure mechanism, and the least con- 

 stant is the scapha-helix. The study of the striking differences in structure 

 exhibited by the auricle in various animal forms reveals the fact that most 

 of their auricular individualities are in the nature of remarkable morphologi- 

 cal adaptations to their varying physical requirements. 



CYTOLOGY. 



Chemistry of the Living Cell. 

 Owing to the industry of the biological chemists, we are fairly familiar with 

 the various chemical substances contained in the cells forming the elements 

 of the body-tissues, but since most of the methods of analysis cause the death 

 of the cell, they have been able to tell us very little of the chemistry of living 

 cytoplasm. The progress made in this laboratory in the development of the 

 methods of tissue-culture has rendered possible an approach toward such a 



