124 Mr. O. H. Latter on the Prothoracie Gland of 
jections or tubes) are groups of parapodial sete. It is 
noticeable as pointing to similarity of origin of these glands 
and tracheal tubes that in many cases the cells are spoken 
of as forming distinct chitinous projections into the 
cavity of the gland and its duct. This is notably the case 
in the duct of the gland of D. vinula, and is very sug- 
gestive of the well-known spiral thickenings of tracheal 
tubes ; at the same time attention may be called to the 
branching nuclei of the cells of these glands and of those 
of the silk-glands which have been claimed as homologous 
with tracheze (Biitschhi, loc. cit.), though much importance 
cannot be attached to this feature. 
Should the significance here claimed for these struc- 
tures prove to be correct, they will go far towards estab- 
lishing the primitive nature of the eruciform larva, of 
which many observers are already in favour. 
i. Tue Presence oF Potassium HypROXIDE IN THE 
ALIMENTARY CANAL. 
In my communications already referred to I have shown 
that the imago of D. vinula discharges potassium 
hydroxide from a sac in connection with the alimentary 
canal. The digestive fluid of the larva being strongly 
alkaline rendered it probable that this fluid was of the 
same nature. In order to test this 1 examined the 
digestive system and the rest of the body with a view to 
finding potassium salts. Twenty larvee were employed 
for the purpose ; their alimentary canals were placed in 
dilute hydrochloric acid, and the remainder of their bodies 
in another lot of the same acid. In both cases I was 
able to determine by the platinum perchloride method 
the presence of potassium, which was also confirmed by 
spectroscopic examination. In the alimentary canal J 
could tind no sure indication of any other salt than the 
hydroxide, but, the remainder of the body appeared to 
contain traces of the carbonate as well. An unfortunate 
accident prevented me from making a reliable quantita- 
tive analysis. 
il, A CoRRECTION. 
I stated in Trans. Ent. Soc. Lond., 1895, p. 403, that 
near the hinder end of the mesenteron of the freshly- 
emerged imago a short wide tube opened from the gut 
