WAITE : ANTENNAL GLANDS IN HOMAPJJS AMEKICANUS. 177 



the appendage. As a result, in a parasagittal section — at this stage a 

 proximo-distal section of the appendage — there is to be seen a single 

 row of cells (Plate 3, Fig. 26, i'vag. ec'drm.). Preceding or following 

 sections of the series usually show that there is an accompanying row by 

 the side of this, i. e. the sheet is two cells wide, and one cell deep dorso- 

 ventrally. In a few cases there is evidence in transverse sections that 

 there are three rows through at least part of its course, these being so 

 arranged that the cross section is triangular. These rows are not dis- 

 tinctly separated but interdigitate, so that the dividing line is anything 

 but straight and sharp, as would be the case were this formation an ac- 

 tual invagination. The line — there is no lumen — between these rows 

 may represent a potential lumen derived from the outside world, but I 

 can trace no actual connection. There is, to be sure, in the region of the 

 connection with the ectodermic wall, a slight depression (Plate 3, Fig. 

 26, fos.) in the surface of the ectoderm, but the cellular arrangement 

 does not warrant the conclusion that this is a real invagination. I be- 

 lieve therefore that the ectodermic ingrowth is a solid plug, and not an 

 invaginated sac. 



As this plug advances along the dorsal (now ventral) face of the endsac 

 and approaches the proximal border, it is subjected to less stress, its 

 proximo-dorsal border being in contact with only the mesenchyme and 

 the fluids of the body cavity. The plug here enlarges ; at first there 

 are in this region one or two extra rows of cells (Plate 3, Fig. 26, i'vag. 

 ec'drm.), — cross sections often show four rows, — a little later the plug 

 enlarges into a knob-like body in which an intercellular lumen appears 

 (Plate 3, Fig. 27, i'vag. ec'drm., hi.). There is no reason to believe 

 that the lumen thus ai'ising is an enclosed part of the body cavity, and 

 there is no evidence to show that it is actually a part of the outside 

 world. I believe that it is a lumen of independent origin, just as is that 

 of the endsac ; but in the case of the ectodermic ingrowth it is inter- 

 cellular, while in the endsac it begins as an tWra-cellular space. 



This ingrowth of the ectodermic plug and its expansion into a knob 

 containing a lumen is a rapid process. I have found all the stages hith- 

 erto noted in the same batch of eggs from a single female, and all killed 

 at the same moment. In September and October this condition is at- 

 tained in about 30 days, probably in somewhat less time in eggs extruded 

 in the middle of summer. 



The condition shown in Figure 27 (Plate 3) progresses distad and 

 ventrad along the ectodermic plug towards the region of its connection 

 with the ectodermic wall of the appendage. The axial line separating 



