Coxal Glands of Scorpio. 7 
On 
duct above described coils. These tubules are bathed in a 
blood-stream, which is brought by a special vessel which 
arises from that accompanying the nerve running into the 
third leg. The blood is conducted by this vessel between 
the anterior layer of the coil of the coxal gland, and is then 
discharged freely among these end-tubules. The histology of 
these tubules differs considerably from that of the main duct. 
The epithelium lining the tubules in Scorpio is apparently 
discontinuous, the cells, containing large nuclei, being irregu- 
larly scattered upon the membranous wall of the tubule 
(figs. 4 and 5). ‘This mass of tubules with the blood-spaces 
between them has been called by Lankester the “ medullary 
substance.” ‘This name, while it applies perhaps to the state 
- of the end-tubules figured by him, which must represent that 
of a very young specimen, is totally inapplicable to the adult 
condition. ‘That this part of the gland happens to be medul- 
lary at all is simply due to the coiling of the main duct 
around its proximal branched portion. In the Chernetide we 
also have the proximal end of the gland surrounded by the 
coils of the duct; but there are no branching tubules such as 
we find in Galeodes and Scorpio. 
No one can examine these end-tubules of the coxal gland 
of Scorpio without being reminded of the end-saccules to the 
antennal and shell-glands of the Crustacea. Sturany sus- 
pected that these tubules represented a typical end-saccule, 
but was unable to prove it. Perhaps I have been more 
fortunate in my sections ; working from before backwards, it 
is easy to find in the anterior sections the blood-spaces in 
connexion with the blood-vessel above described. he actual 
opening of the blood-vessel into the blood-spaces is much 
disguised by a peculiar group of cells (PI. IL. fig. 4, c), between 
which the blood seems to flow. In these sections the blood- 
spaces are more conspicuous than are the tubules. In the 
posterior sections the connexion between the main duct and 
the tubules is also easy to find (fig. 5). 
The transition between the scattered epithelium of the end- 
saccule and the specialized striated epithelium of the main 
duct I have endeavoured to show in fig. 5. 
The presence of typical end-saccules at the proximal ends 
of the coxal glands of Galeodes and Scorpio has an important 
bearing on the morphology of the antennal and shell-glands 
of the Crustacea. In the first place, it is difficult to doubt 
that these are all homologous structures; the extraordinary 
histological likeness between the main ducts and their common 
development of end-saccules seems to me to render the 
homology almost certain. ‘lhe great importance of this 
homology, however, lies in the fact that the end-saccule in 
