58 A. ©. OUDEMANS. 
for they have very thick walls. I have examined the prepara- 
tion very closely, but I did not see any more ducts. Thus, in 
this species, there is but one single pair of ducts, not in the 
posterior part but quite anteriorly. In front of the excretory 
ducts there is no trace of nephridial system. I have no 
histological facts to record. 
14. Amphiporus lactifloreus (Johnst.), McInt., figs. 9, 
10, 388—40. 
The mouth and the proboscidian sheath have together only 
One aperture, nearly terminal and on the ventral side. This 
was first seen by Prof. Hubrecht, who noted it down on his 
preparation. I saw very distinctly in this preparation that the 
proboscidian sheath falls into the stomodzum ; and this is, as 
we know, not behind but far before the ganglia. Above this 
stomodeum, thus also above the proboscidian sheath, goes the 
loop which unites the two vessels of the head (fig. 9). Of this 
loop we at first observe an ellipsoidal lumen, then a dumb-bell 
shaped one; and, finally, two lumina, being the transversally 
cut vessels. These two are gradually placed wider apart. 
Their wall consists of a very thick hyaline basal layer. They 
finally lie laterally to the proboscidian sheath and the eso- 
phagus (fig. 38). 
The brain respirators are very small. Their aperture is the 
foremost part of the whole organ. (They lay in the slice 
No. 31. The slices had a thickness of ;mm. The specimen, 
in spirits, measured 17 mm. in length and 2 mm. in thickness.) 
The canals run backwards, lying beneath and contiguous to 
the vessels. A thick nerve-stem connects them with the 
ganglia. They soon disappear (slice No. 41). 
The blood-vessels go upwards (No. 37), just before the lower 
brain commissure, between the two brain-masses and the 
proboscidian sheath ; but in their former place they have left 
two remnants which soon disappear (slice No. 42). These two 
terminate thus blindly posteriorly (see fig. 9). Exactly above 
the lower brain commissure the vessels move beneath the 
proboscidian sheath, unite, and communicate with the dorsal 
