292 
S1DNET F. HARMER. 
portion to form the "gland,” the "duct” of the organ 
remaining throughout life fundamentally in its embryonic 
condition. In fig. 37 the dorsal organ ( br ) is seen, contrary 
to the statements of Hatschek on Pedicellina to consist of 
a few columnar epiblast cells. The section in question is 
only one of a considerable number, giving the same evidence 
as to the earliest development of this structure. From its 
position there cannot be any doubt that the epiblastic thicken- 
ing is correctly identified as the dorsal organ, which neither 
in its earliest appearance nor in its ultimate fate shows the 
slightest evidence of its supposed function as a bud-producing 
organ. At the earliest stage at which it is possible to identify 
the dorsal organ with certainty, it invariably consists of a single 
layer of cells forming part of the one-layered body wall, and 
there can hence be no question as to its epiblastic nature. 
One further point may fairly be urged against Hatschek' s view 
of the developmeut of his " Entodermsackchen.” According 
to Hatschek certain hvpoblastic cells are budded off from the 
anterior wall of the mesenteron ; they enter into connection 
with an epiblastic thickening, with which they form a budding 
organ, the endoderm cells of the bud being derived from the 
hypoblastic mass, which has taken origin from the walls of the 
mesenteron. My own sections lead me to believe that the 
stomodaeum extends inwards a greater distance than was sup- 
posed to be the case by Hatschek in Pedicellina (see figs. 
37 and 38), and if my view is correct the dorsal organ makes 
its appearance opposite a portion of the stomodaeum. This 
being the case, judging from Hatschek's description, the first 
cells forming the dorsal organ, and occurring between the epi- 
blast and the hypoblast, are derived from the epiblastic cells 
of the stomodaeum, and this hypothesis refuses to adapt itself 
to Hatschek’s own view on the nature of the budding process. 
Finally, I must state that I have satisfied myself, by means of 
sections, that even in the embryos of Pedicellina the dorsal 
organ first appears as a thickening of the epiblast. 
In order to prepare the way for the following description 
of the further history of the development, I may at once state 
