178 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



the cell rows is now distinct and even, and quite different from the line 

 separating the two interdigitating rows of earlier stages. This axial line 

 represents a potential lumen, and by separation of the apposed walls the 

 lumen is formed here at later stages. Figure 28 (Plate 3) is a parasa- 

 gittal section from an embryo about 35 days old. The endsac (sac. trm.) 

 has its cell walls well marked and the lumen (lu. ) is sharply bounded. 

 The ectodermic ingrowth (ivag. ec'drm.) shows in longitudinal section 

 two rows (many rows in all) to a point near the distal end of the endsac. 

 The cells are more columnar than in earlier stages. Some of the ecto- 

 dermic cells of the wall of the appendage are much elongated. They go 

 to form the ligaments seen in this region in later stages. 



Figure 29 (Plate 3) is a transverse section at a little later stage (about 

 40 days, September 10th to October 20th). Here the lumen of the ecto- 

 dermic plug (i'vag. ec'drm.) is evident and can be traced to the exterior 

 (of. ex.). This duct has arisen as the outward extension of an intercel- 

 lular lumen, first appearing in the region of the deep proximo-dorsal end 

 of the ectodermic plug. 



There is thus formed in the embryo of about six weeks an endsac with 

 definite lumen, and an ectodermic ingrowth with lumen, and with a duct 

 opening to the outside world, but these two lumina are not in connec- 

 tion. The duct of the ectodermic ingrowth persists as the permanent 

 duct of the adult organ. However, its lumen is not always visible, espe- 

 cially in the deeper regions, for the growth and resulting pressure at 

 times apparently obliterate it by causing a close apposition of the walls, 

 which, however, do not actually fuse, for at all subsequent stages when a 

 section in the region is torn the lumen is reopened. 



There are still two important points to be determined in the embry- 

 ology of the antennal gland. When, and at what point, does the lumen 

 of the endsac become continuous with that of the ectodermic sac? In a 

 series of embryos taken from a female kept in confinement during the 

 winter (see Herrick, '95, No. (3) 18, Table 18, p. 56) I find that in those 

 killed April 1st (estimated age 273 days) the lumina are separate, but 

 in embryos of the same series killed May 1st (estimated age 303 days) 

 the lumina are continuous. The details of the union of the two lumina 

 I am unable to describe, as I have no intermediate stages. 



For some time before this last stage is reached, the lumen of each part 

 is seen in sections, but the two lumina are separated by the closely ap- 

 posed walls of the two sacs (Plate 3, Fig. 31 ) . The break through the two 

 walls occurs on the dorsal face of the proximal region of the endsac and 

 at the terminal end of the ventral part of the forked proximal end of the 



