COLLAR CAVITIES OF THE LARVAL AMPHIOXUS. 245 
Material and Method. 
Four larval stages were examined. Larvae which had been 
fixed in Hermann's fluid were obtained from the Naples 
Zoological Station. They were cut into series of transverse 
sections by the method of double embedding in celloidin and 
wax, and the sections, 4 /u or 5 u thick, were stained variously 
with Delafield’s liasmatoxylin, thionin, alcoholic haematein ; 
or with an aqueous solution of picro-nigrosin for the special 
purpose of making plain the relations of the myosepta. 
It is, as other workers have found, difficult to obtain 
perfectly preserved material ; larvae of the same batch 
apparently vary in their reaction to the fixative. To obtain 
reliable results it was found necessary to section a large 
number of animals, discarding those which showed distension 
or contraction, and basing conclusions on those alone in which 
the histological detail was convincing. 
Our drawings are, to the best of our ability, faithful 
reproductions of the appearance of the sections, except that 
in some of them the irrelevant cytological detail is omitted. 
They were all made at the level of the microscope stage with 
the aid of a camera lucida, the magnification being, in each 
case, that obtained with a 2 mm. apochromatic oil-immersion 
objective and No. 6 compensating ocular of Leitz. 
Description. 
The earliest stage examined was one in which the larvae 
show as yet no indication of the formation of a mouth. The 
left head cavity is a vesicle unconnected with the ectoderm — 
though in contact with it — the club-shaped gland opens 
widely into the floor of the enteron, and the endostyle 
appears as a slightly thickened area of the right side of the 
swollen pharyngeal region. The formation of somites from 
the archenteron is still occurring at the extreme posterior 
end of the animal, and the tail has not begun to grow. 
In such a larva the cavities of the collar somites have no 
