444, A. A. W. HUBRECHT. 
the mesoblast, and have only to add a few words concerning 
the further development of the cellular layers of the epiderm. 
The outer layer, i. e. the secondary epiblast, retains its character 
as an embryonic layer for a very long time, although in a 
very early stage vacuolation may be noticed in a large majority 
of these cells (1. c. (30), pl. iv, figs. 63, 64), followed by a 
change in their elements into distinct, flask-shaped unicellular 
glands, such as are so copiously present in the epiderm of the 
adult. The remaining cells carry the numerous cilia, which in 
the very early stages can be distinctly noted to be separated 
from the body of the cells by a most distinct transparent 
cuticula. Whether the deeper glandular layer, which is also 
very characteristic in the adult, also arises out of this same 
layer of secondary epiblast, could not be ascertained beyond all 
doubt ; it appears, however, very probable. 
Another derivative of the epiblast are the generative sacs, 
although with respect to these I cannot speak with absolute 
certainty. I find the embryonic generative sacs—right and 
left and interccecal—connected with the epiblast by a bridge 
of tissue which cannot be the earliest condition of the ejacu- 
latory ducts because those outer openings and their ducts lie 
dorsally of the lateral nerve stems, whilst on the contrary, 
these embryonic connections are found below the nerve stems 
(l. c. (80), pl. v, figs. 88 and 89). Moreover, the con- 
nections disappear in older stages and the definite ducts and 
openings must undoubtedly arise de novo. However, I have 
no preparations of the very earliest stages of the development 
of the generative sacs, so that as yet I can only invoke great 
probability, not certitude, about their actual origin out of the 
epiblast. 
