ON THE LAMINAR TISSUE OF AMPHIOXUS. 
427 
and are separated from one another by transverse partitions 
(see fig. 5), which are very thin.^ The whole cavity, the 
papilla as well as the walls, is lined with a layer of cells, 
which closely resemble those lining the other spaces ; there 
is no appreciable difference between the cells on the papilla 
and those on the walls. The contained liquid seems to be 
the same as that in the other spaces. 
In the living animal the substance of the papilla can only 
be distinguished from the ambient liquid by the optical effects 
due to their differing density. In a specimen which has 
been preserved in alcohol the papilla had almost disappeared. 
Certain reagents have the same action, whilst others appear 
to swell them up. If the specimens are put into alcohol, 
even after the action of osmic acid, the papilla are altered in 
shape and drawn in. Their surface presents depressions, 
which gives them a jagged appearance in section.^ 
The use of reagents brings to view minute cavities inside the 
papilla, more or less irregular, and about the size of one of 
the nuclei. Suitable methods show that the amorphic sub- 
stance of the papillae contains nothing but some very fine and 
scattered fibres. Transverse sections (fig. 4) show very well 
the relations of the papillae. There is a fibrous lamina occu- 
pying the middle line of the body, which, bifurcating at the 
level of the upper edge of the two lateral muscular masses, 
joins on each side the subcutaneous aponeurosis. The base of 
the papilla rests in the groove formed by this bifurcation, and 
is clearly marked out by its physico-chemical characters. The 
cavity which it contains, is itself bounded laterally and below 
by the subcutaneous aponeurosis. 
The papilla is traversed towards its base by a layer of very 
fine fibres (fig. 4, c.) stretched between the two fibrous 
laminae. In front and behind (fig. 5, c.) this sheet of fibres 
becomes raised up before being inserted into the partitions 
which separate the cavities. On the upper face of the 
layer a very loose and irregular network of extremely fine' 
laminar fibres rise up and spread out in the centre of the 
papilla. None of these are directed downwards. When 
treated with osmic acid and then saturated with picro- 
carmine, the substance of the papilla assumes a slightly 
greenish tint, and moreover becomes slightly granular, and, 
* Ant. Schneider, who believes tliat these cavities communicate with the 
system of canals, describes the latter as bounded by a membrane, with 
nuclei and finely striated fibres, and calls these fibres “ muscular (?),” loc, 
cit., pp. 8, 9. 
- This it is which Ant. Schneider (loc. cit., p. 8) has described as stalked, 
and supposes them to be contractile ! 
