the cells are arranged around the lumen in a one- 

 layered epithelium. i'^ . 2. 



Fig. 30. Median sagittal section of a bud at about the stage 

 of Pig. 4, shov/in;':^ the position and extent of tne 

 dorsal tub«^ . ""ne peribranchial cavity is not yet 

 completely constricted off from tne branchial sac. 

 j;. 2. 

 7ii~. ^1 -_'^i_b,_c,_d , and _e . Transverse section shov/ing the 

 devrlopment of the ganglion. Tn a and _b a few 

 cells resembling . lesodermal cells are seen lying 

 * on the dorsal side of tne dorsal tube. The wall 

 of the latter is broken at this point, and nuclei 

 appear to be wandering out into the rudiment . In 

 £ and _d the rudiment is much enlarged, and in tne 

 latter trie nuclei are beginning to arrange tnera- 

 selves in peripheral region vf tne rudiment. In 

 _e the wall of the dorsal tube under the ganglion 

 has been reformed, and the central portion of tne 

 latter is now free from nuclei and occupied by fine 

 fibrils. P. 2. 



Figs. 32, £, b, and c_. Sections illustrating the early de- 

 velopment of tne sexual organs. Tn a an early 

 stage is shovm, when the rudiment is merely a loose 

 mass of cells, surrounding a slight cavity. A 

 couple of tne elongated cells v/hich will form the 

 genital cord are also ser-n. In b the cavity of 

 the rudiment is much enlarged, and the genital cord 



