would seem probable, then, that Lacaze-Duthiers's M. tubu- 
het than Hugyra arenosa, and consequently does 
not belong to the genus Molgula. 
. M. Lacaze-Duthiers's discovery, however, is not the less 
Interesting on that account, It is a matter fraught with much 
importance, as it seems to establish the fact that the Tunicate 
organization can be developed without passing through the 
_ tadpole-condition—or, in other words, that this condition is 
non-essential in the development of this molluscous group. 
When Lacaze-Duthiers's memoir is published in full, it wi 
be time enough to speculate on the effect his discovery may 
have on the recent investigations and theory of Kowalevsky 
respecting the relationship of the Tunicata to the Vertebrata. 
-I shall avail myself of the present opportunity to describe 
several new species of the Simple Ascidians, some of which 
were determined before Mr. Alder’s death, others since that 
sorrowful event, by myself: the former will stand in our joint 
names ; for the latter I am alone responsible. 
Ascidia plana, Hancock. 
