OF OECANTHUS AND TELEAS. 247 



The stomodaeum (pi. 19, figs. 2, 4 and 13; pi. 22, fig. 1; Fig 25) early assumes 

 a tubular condition, but it does not unite with the mesenteron until after the closure 

 of the body walls. It extends from the mouth opening back into 

 the region of the second thoracic segment, and in its growth pushes 

 itself into the mesenteron, carrying before it the wall of the mid gut. 

 The portion of the mesenteron which projects in front of the posterior 

 end of the stomodaeum is subsequently converted into the pyloric caeca 

 of the adult animal. Like the proctodaeum, the stomodaeum ends 

 blindly at first, but its cap is not so marked as that of the former. At 

 the time of revolution there appears a pocket in the median dorsal line 

 OpticaTsagittai sec- similar to that formed in the proctodaeum for the Malpighian tubes. 

 before% pr MaS^ghS Th e fete of this pocket is unknown. Upon the union of the stomodaeum 

 vessels arise. x25o. ^^ t ^ e mese nteron, the alimentary tract is converted into a continuous 

 tube. In cross sections of the embryo one finds the epithelial layer of the stomodaeum 

 thrown into six longitudinal folds, which at first nearly fill its lumen ; but by its subse- 

 quent increase in circumference they are reduced to ridges along the inner surface of 

 the canal. In the anterior portion of the stomodaeum the dorsal fold is larger than 

 the others and is frequently bilobed. (Compare the sections shown in pi. 21, fig. 37 • pi. 

 22, figs. 11, 15; pi. 23, figs. 1, 2, 4.) The stomodaeum passes through the nervous cord 

 between the brain and first ventral ganglion. The invagination for the alimentary tract 

 having taken place before the formation of the nervous cord, the latter is in consequence 

 compelled to grow around the stomodaeum in order to unite with the brain. The 

 stomodaeum forms, by an enlargement near its posterior termination, the proventriculus. 



Although the salivary glands arise as invaginations of the ectoderm (pi. 23, fio-. 1) f 

 the ventral surface of the mandibles, yet they soon come to unite with the oesophagus by 

 a common duct (pi. 18, fig. 16) and, from the subsequent shortening of the oesophagus, to 

 empty into the floor of the mouth. The invaginated portions extend upward toward the 

 dorsal line of the body in the form of a solid, curved rod of thin-walled spindle-shaped cells. 

 The nuclei of these cells are equal in size to those of the ganglionic cells and besides exhib- 

 iting a distinct nucleus, they are connected with the central fibre of the rod by what is 

 apparently a portion of the nuclear membrane. The rods are ultimately directed backwards 

 and reach into the abdominal cavity. A short distance back of their union into a common 

 duct, each gland bifurcates. They never become convoluted as do the Malpighian vessels. 

 Before hatching, all trace of their origin has disappeared. No evidence of the existence of 

 the spinning glands of other groups was found at any time, although I have carefully stud- 

 ied my preparations of the early stages for the invagination in the upper lip from which 

 they arise, and those of later stages for the glands themselves. The uniform result has 

 been the failure to detect any structure that could be interpreted as belonging to these 

 organs. 



The part of the mesenteron (pi. 19, figs. 4 and 5 ; pi. 22, fig. 1) which is first formed 

 within the body of the embryo is a sheet-like extension of endodermic cells alon°- the 

 germinal band in contact with the yolk. It is pushed away from the head region by the 

 growing stomodaeum and from the posterior abdominal region by the proctodaeum, so that 

 it is confined to the thoracic and anterior abdominal segments. In the region of its con- 



