NOTES ON THE STRUCTURE OF OIKOPLEURA. 51 
a few sections the endostyle becomes again shut off from 
the pharynx, so that the opening between the two is very 
small and the greater part of the endostyle is not a canal 
as in most Tunicata, but a closed in tube (compare PI. 
IV. fig. 9, en.). Its close resemblance both in transverse 
(P1. IV. fig 3) and in longitudinal (fig. 9) section to its 
homologue the thyroid involution in the larval lamprey is 
more marked in this form, I think, than in any Tunicate 
yet figured. This endostyle differs considerably from that 
of Vexillaria speciosa as figured by Kisen. 
Twenty sections further forward (Pl. IV. fig 4) we find 
the body greatly reduced in size, as we are now not far 
from the anterior end; while the tail is still very large. 
The branchial sac or pharynx is small and is transversely 
elongated. Above it we find the nervous system now 
becoming of considerable size, and ventrally is the closed 
. endostyle composed of large glandular cells arranged below 
a small circular lumen. 81x sections further forward (Pl. 
IV. fig. 5) we find the body and the branchial sac still 
smaller, the endostyle large but with no lumen now, and 
the nervous system larger than before with the otocyst 
attached to it, on the left side. On each side of the bran- 
chial sac is seen a large glandular mass which is the 
posterior end of an elongated cylindrical or sausage shaped 
closed gland lying at the side of the mouth (PI. IV. fig. 5). 
This section shows also the very large ciliated infundi- 
bulum (fig. 5, d.t.) which opens into the dorsal edge of the 
branchial sac, on the right side, and which probably corres- 
ponds to the opening of the hypophysial duct on the dorsal 
tubercle of an Ascidian. A few sections further forward, 
in No. 257, we see this organ still better, and the middle 
portion of this section is shown more highly magnified 
(x 600) in Pl. IV. fig. 6. The pharynx is thin walled and 
irregular in shape with the ciliated funnel opening into the 
