A NEW GENUS OF SYNASCIDIANS FROM JAPAN. 319 
not the slightest reference to them in the text, except in so 
far that he follows von Drasche in giving the appearance of 
“yudimentary embryonic blastogenesis ” as a characteristic 
for the group. We will not deal with these tentacle-like pro- 
cesses any further at present, as one of us has recently been 
following their occurrence and relations in another group of 
Ascidians, namely, in the Styeline; and we will therefore 
defer the discussion of them. Suffice it to say that far from 
being connected with any budding process, they are, both in 
Didemnide and in the Styeline, transient larval appendages, 
which become reabsorbed in the course of development. 
In the Botryllidz, on the other hand, according to Metschni- 
koff (‘ Bull. de Acad. Imp. des Sciences de St. Petersburg,’ 
t. xiii, 1869), they persist and give rise to the well-known 
vascular processes with swollen extremities which traverse the 
test of the adult colonies. 
How the larve escape from their lodgment in the test is 
not quite clear. We may assume a process of absorption or 
possibly rupture, but neither can be asserted. The probability 
is that both occur. The larve can only sink into the depths 
of the test accompanied by a process of absorption, and when 
they are only separated from the central canal by a thin layer 
of test their movements could easily rupture that, and they 
could thus escape through the excurrent orifices. 
5. Structure of Test—Spicules. 
The deeper parts of the test contain numerous pigment 
concretions, and in the more superficial region there is a thin 
layer of extremely delicate calcareous spicules. 
Although the presence of spicules is not an absolute feature 
of the Didemnide—since von Drasche has described two 
species of Didemnum, and Herdman one, in which spicules 
were absent; and, again, von Drasche has described a species 
of Diplosoma with spicules—yet combined with the other cha- 
racters mentioned above, and especially with those belonging 
to the larve, the presence of spicules may be taken as a 
decisive feature in assigning the new genus to the family of 
