PHYSIOLOGY OF ASCIDIA ATRA LESUEBUR 241 
mucus catches the food particles which come in with the water, 
and the mixture: of food and mucus is transported across the 
face of the branchial sac, dorsally and posteriorly into the 
oesophagus. In recent textbooks (Herdman, ’99) the process 
is described in a totally different way, somewhat like the fol- 
lowing. The mucus from the endostyle passes anteriorly to the 
peripharyngeal grooves. Here the food particles are caught at 
their very entrance to the branchial sac, and carried by the 
mucus on its way along the dorsal lamina to the oesophagus. 
Delage et Herouard (’98, p. 144) point out the differences in 
these descriptions, but cautiously avoid anything but a general- 
- ized account of feeding. 
The matter has been recently investigated on many transparent 
ascidians by Orton (713), who has proved very clearly that the 
earlier accounts are correct. “I have examined the process of food 
collection in Ascidia and in the transparent Ecteinascidia tur- 
binata, and my observations are in complete agreement with those 
of Orton. Occasionally specimens of A. atra are found which 
are quite translucent. By feeding carmine to such animals, it 
is possible to see the red band of mucus-entangled material 
swept along the branchial sac, upward and backward into the 
oesophagus. 
The mechanism by means of which the transportation is 
accomplished deserves a closer scrutiny. At regular intervais 
along the junctions of the transverse and longitudinal vessels 
of the branchial sac, there are present small papillae which pro- 
ject into the cavity of the sac. A papilla is really the wall of 
a blood sinus, and in A. atra its ventral wall is composed of a 
ciliated epithelium (fig. 4, A). At its junction with the inter- 
secting vessels, I have always found a flat semicircle of what 
seems to be smooth muscle cells (fig. 4, B). The location of 
the ciliary surface of the papilla and the muscle at its base are 
intimately concerned with the collection and movement of the 
food. 
By removing a part of the test and branchial sac, it is easy 
to observe with a binocular microscope the function of the 
papillae. Food particles which are filtered by the meshes of 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, NO. 1 
