264 



CHARLES RUSSELL BARDEEN. 



in brief outline the assumption by the embryo of the form char- 

 acteristic of the adult. 



In Fig. i are shown four stages in the development of the 

 embryo. These figures were sketched by means of a camera 

 lucida from living specimens. The outline of the intestinal cav- 

 ity, as it appeared by transmitted light, is shown by serrated 

 lines. In D the septa extending into the intestinal cavity are 

 represented more highly developed than is common at this stage. 



B 



FIG. I. Various stages in the development of the embryo. Magnification, 57 

 diameters. 



A. Dorsal view of an embryo in which the anlage of the permanent pharynx is 

 being developed. At the right the opening into the embryo-pharynx is shown. 



B. Ventral view of an embryo in which the pharynx has begun to assume 

 definite form. 



C. Ventral view of an older embryo in which the two posterior extensions of the 

 intestinal cavity have united behind the pharyngeal pocket. 



D. Dorsal view of an embryo at the period when the central nervous system has 

 assumed definite outlines. 



' This was done so as to expose the nervous system. The latter 

 was reconstructed from sections made from the embryo. In A 

 the opening into the embryo-pharynx is shown at the right. In 



