A NEW GENUS OF SYNASCIDIANS FROM JAPAN. 315 
other Didemnids in the fact that its height or thickness in 
the vertical direction exceeds two- or three-fold the width, while 
in other forms the thickness or vertical height of a colony is 
usually very small. Our genus agrees with all other Didemnide 
in being sessile, but differs from most of them in not forming 
encrusting or straggling masses. 
Beyond the characteristic lobes and the upraised margins 
of the excurrent orifices there are no processes of any kind on 
the external surface of the colony. 
2. Canal-System. 
The canal-system of the new genus bears a general resem- 
blance to that found in other forms of the Didemnidz, but in 
its extent and elaboration stands alone. 
A schematic representation of the system of canals is given 
in fig. 1, while an actual transverse section is shown in fig. 2. 
It will be at once evident that the canal-system consists of 
a peripheral portion and a central portion. The peripheral 
portion consists of much-branched canaliculi, whose ultimate 
extremities lead from the atrial apertures of the Ascidiozooids 
(fig. 3), and then open into larger canals, which again discharge 
into the large central spaces from which water and excrement 
are conducted through the excurrent orifices to the outer world. 
It will of course be borne in mind that these so-called ‘‘ canals” 
are only irregular spaces excavated in the mass of the common 
test, and having nothing in the shape of an epithelial lining, 
although the cells in the test are very numerous, and often are 
so arranged as to present a deceptive resemblance to a flat 
epithelium. 
As already mentioned, the incurrent orifices consist of the 
pores leading to the branchial apertures of the Ascidiozooids 
(fig. 3). These (i. e. the Ascidiozooids) are some little distance 
removed from the surface of the colony, so as to give rise to a 
veritable incurrent canal. 
It is thus seen what a justifiable analogy may be drawn 
between these Ascidiozooids and the ciliated chambers of a 
sponge; in other words, between individuals on the one hand 
