COLLAR, CAVITIES OE THE LARVAL AMPHIOXUS. 
25 L 
ch. Notochord, c. g. Club-shaped gland, esty. Endostyle. 1. c. s. 
Left collar somite. 1. h. c. Left head cavity. 1. m. 2. Second myotome 
of the left side. 1. me. 2. Second myocoel of the left side. m. Mouth. 
n. c. Nerve cord, r.c.s. Right collar somite, r.h.c. Right head cavity 
r. m. 1. First myotome of the right side. r. m. 2. Second myotome of the 
right side. r. me. 2. Second myocoel of the right side. s. Septum. 
spl. Splanchnocoel. t. me. Trunk myocoel. 
Fig. 1. — Transverse section through the pharyngeal region of a very 
young larva, showing the relations of the collar somites to the gut. 
The section is 4 y thick and was stained with tliionin. Note the 
separation of the outer wall of the right collar somite from the 
ectoderm. 
Figs. 2-7. — Transverse sections through the pharynx of a larva in 
which the mouth is just formed. Figs. 2-5 are of consecutive sections ; 
between 5 and 6 one section is missed, between 6 and 7 three sections 
are missed. The preparation from which the drawings were made was 
overstained, in picro-nigrosin to make plain the septa, and this has 
obscured the cytological detail. For further description see text. 
Fig. 8. — Diagrammatical representation of the relations of the coelomic 
spaces of the left side of a larva in which the mouth is just formed , 
The dotted lines show the condition on the right side where the wide 
opening of the collar somite to the splanchnocoel is not interfered with 
by mouth or head cavity. 
VOL. 62, PART 2. N liW SERIES. 
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