TAIL-EKGIOX OF POLISTOTKEMA (p>l)EL1.0ST0.^[A) STOUTl. 319 
sinus was observed in the 85 imn. series, and liow many of 
them occur in the 10 cm. series I am unable to state, since I 
have not sectioned an adult anterior of the last two mucous sacs. 
Dorsal Veno-lym pha tic Trunk (Figs. 1 and 4, D. V .). — 
Has much in common with the ventral veno-lymphatic trunk 
already described. In a transverse section (Fig. 1) it will be 
seen in a median line, between and a little above the level of 
the dorsal end of the myotonies. In the region of the caudal 
hearts it is situated directly above the median dorsal 
cartilaginous bar; immediately in front of the caudal 
hearts its position becomes more dorsad of this bar, 
and anterior of the dorsal fin it ti’avels as a sinus in 
the centre of a connective tissue septum that joins the 
two great lateral muscles. Its cephalic termination I 
have not determined, but posteriorly it terminates, like 
the ventral trunk, at the distal end of the caudal carti- 
lage by sending off a large anastomosing branch to each 
lateral sinus. Also, like the ventral trunk, it is paired in the 
region of a cartilaginous ray and a single trunk between two 
rays, and throughout itsends off many connections to both lateral 
sinuses. The dorsal veno-lymphatic trunk is undoubtedly 
homologous to a similar trunk found in Scorpaenicthy s 
and Lepi SOS tens (Lepidosteus), more closely allied to the 
latter, but less siguilicant, in that it does not receive branches 
from the dorsal fin; these in Polistotrema terminate in 
the lateral sinuses. 
Lateral A^eno- lymphatic Trunks or Sinuses (Figs. 1 
and 2, R. and L. L. S .). — The enormous sinus-like condition 
of these trunks in Polistotrema is very different from any- 
thing found in the Selachians, Ganoids, or Teleosts, but is 
suggestive of the lymphatic sacs of the Amphibia. If the 
entire region drained by the lateral trunks and their inter- 
seo-meutal branches in fishes was united in a common sinus 
O 
covering the entire outer surface of the myotomes, and 
collectino: the branches from the median fins, we would have 
n condition similar to that found in Polistotrema. 
The limits of this sinus may be described as occupying 
