COLLAR CAVITIES OF THE LARVAL AMPHIOXUS. 243 
A Note concerning the Collar Cavities of the 
Larval Amphioxus. 
By 
K. M. Smith, A.R.C.S., 
And 
II. Q. Newth, 
Demonstrator in Zoology, Imperial College of Science and Technology. 
With Plate 18. 
Introduction. 
Notwithstanding the great volume of literature dealing 
with the development of Amphioxus, there are many points 
still outstanding on which the light of further investigation 
must he thrown. The present short communication attempts 
to dispose of one of these. 
It is well known that in Amphioxus the cavities of the 
typical somites give rise, on the one hand, to all the myocoels 
except the first pair, and, on the other hand — by the fusion 
of their ventral moieties on each side — to longitudinal spaces 
which are the splanchnoccels. But the fate of the so-called 
“ collar cavities has not hitherto been satisfactorily estab- 
lished. It was known that from the walls of their dorsal 
parts were formed the first pair of myotomes ; but there has 
been difference of opinion about the behaviour of their ventral 
parts. 
MacBride (1) at first maintained that "the metapleural 
‘ lymph canals ’ found in the atrial folds are the persistent 
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