THE DEVELOPMENT OF THE TEMNOC'EPHALEHL 431 
section of being' pierced by an exceedingly fine, perfectly 
clean-cut canal. How these canals end I have not been able 
to determine: but subsequent stages show that these, with 
the cells that contain them, are the foundations of the excre- 
tory system. 
At first these perforated cells are widely separated from 
the endocoele cavity and embedded in the thickness of the 
blastoderm. As the cavity increases in size their relative 
position becomes altered, until they come to lie directly 
below the lining meinbi'ane of the cavity. At first the entii'e 
structure consists on each side of two cells, a larger and a 
smaller, which have fused, and the substance of which has 
become perforated by a sinuous canal. This is destined to 
give rise to the terminal sac of the excretory system. The 
canal extends through several cells situated close to the first 
two, and in this way is formed the beginnings of the main 
longitudinal vessels. Later (PI. 25, fig. 17), when the rudi- 
ment of the brain has become well advanced, the terminal 
sacs, while still retaining their position immediately under — 
i. e. external to — the membrane lining the cavity, and, while 
still continuing each to consist of only two fused cells per- 
forated by a canal, assume a more complex structure, and 
take on, in all the most essential points, the structure which 
we have found to chai-acterise them in the adult. The canal 
becomes wider in relation to the thickness of the enclosing' 
wall ; and from the main vessel is given off a slender branch 
— the future vesicular vessel — which, approaching' the terminal 
sac on the inner side, breaks up into a nnmber of excessively 
fine capillaries that ramify through the substance of the wall 
of the sac. 
It will be seen from the above account of its mode of 
formation that the excretory system of Tern no cep ha la 
is, in the strictest sense, of intracellular character. I am 
thus compelled to dissent from Goto’s opinion (4, p. 71) that 
I was not justified iu using that term, as well as to his more 
general view (p. 74) that “the term intracellular is quite in- 
voL. 54, PAirr 3. — xkw sekies. 31 
