Coxal Glands q/" Scorpio. 57 



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 ditfers 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 

 (Hgs. 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, wiiich must represent that 

 of a very young specimen, is totally inapplicable to the adult 

 condition. 'J'hat 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 Chernetidge 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 nnd 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. ISturany 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 witli the blood-vessel above described. The actual 

 opening of the blood-vessel into the blood-spaces is much 

 disguised by a peculiar group of cells (PI. II. 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 antenual and shell-glands 

 of the Crustacea, in tiie 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 ine to render the 

 homolugy almost certain. The great importance of this 

 homology, however, lies in the fact that the end-saccule in 



