ON THE LAMINAR TISSUE OF AMPHIOXUS. 
429 
When one observes the gradations of structure between 
these cavities, the small separate cellular cavities placed at 
the extremity of the cord, the terminal cavities of certain rods, 
and, lastly, the rudimentary cavities in the swellings of the 
network in the neighbourhood of the mouth, one is led to 
regard these various structures as the first indications of a 
system of serous cavities and lymphatics. Besides this, the 
cellular lining of these cavities has quite the characters of the 
lining of the embryonic serous sacs in the higher Vertebrata. 
We confine ourselves to merely suggesting this as a probable 
analogy, as we have no exact account of the histogenic 
development of these parts. 
Lastly, what morphological signification shall we give to 
the organ represented by the papilla and its cavity 
Here all terms of comparison leave us completely at 
fault ; no homology whatever among vertebrates is to be 
thought of.^ Their number corresponds neither with that of 
the spinal nerves, nor with that of the myotomes ; they are 
about three or four times as numerous. 
The connection which certain authors put forward^ be- 
tween the papilli and the fin-rays* ought rather to be con- 
sidered as an analogy than a true homology. Amphioxus 
is not altogether devoid of either cartilage or bone. It is 
cartilage which forms the skeleton of the oral tentacles ; 
it is bony substance which forms the framework of the 
branchial skeleton. The papillae, looked at from the point 
of view of general anatomy, would form a third kind of 
skeleton element. They would represent a first stage in 
the differentiation of amorphous matter which is about to 
form a special organ. 
It should not be forgotten that amongst Teleostean fishes 
a certain number of bony organs of the dermal skeleton 
result simply from a similar differentiation of amorphous 
intercellular substance, such as we have shown in the bony 
plates of Syngnathians. In the latter case, the amorphous 
matter becomes individualised as calcareous salts are de- 
posited in it ; in the papilli of Amphioxus fatty matters are 
no doubt deposited in it. In any case, both belong directly 
to a numerous and varied group of amorphous intercellular 
substances. 
’ We may here note a peculiarity which presents itself in the sheath of 
the notochord of Amphioxus. In the most successful transverse sections 
this presents above a slight median prominence (cf. Ant. Schneider, loc. cit., 
pi. XIV, fig. 1), and below two slight prominences on each side of the 
median line, which no doubt might be considered as the first rudiments of 
the vertebral skeleton. 
2 Anton Schneider, loc. cit., p. 8. 
VOL. XX. NEW SER. 
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