28 
Journal of the 
and one of these— A. divaricata , Busk—has open corbulre resem¬ 
bling those of A. McCoyi. An interesting form from Port 
Darwin has a lenticular gonotheca on every third pinna of eacli 
series, borne near the base; the pinna, which bears, instead of 
hydrothecse, two series of sarcotheca), being recurved and directed 
forwards in such a manner as to generally overarch the next 
gonotheca in front, the separate elements of the corbula being 
thus scattered along the stem, instead of being combined on a 
single branch. This species also is provided with sarcothecse 
with two orifices. A. parvula usually lias the mesial sarcotheca 
channelled in front,* in other words, the lateral and terminal 
apertures are united by an opening more or less wide. Some¬ 
times, however, this opening is represented by a mere crack in 
the cliitinous tube. The transition to this form from those with 
two distinct apertures is well shown in A. prolifera. In that 
species the mesial sarcothecae are normally somewhat longer than 
the hydrotliecae, and have two distinct orifices; but when, as 
often happens, they are considerably shortened, the two apertures 
become completely confluent, forming the so-called canaliculate 
nematophore. In those of intermediate length, the two orifices 
are connected by a crack or slit. 
I am not aware whether any author has alluded to the presence 
of more than one-aperture in the lateral sarcotheca), but nearly 
all the species that I have been able to examine are furnished 
with two, or in some cases with three. Usually there is a sub¬ 
tubular terminal orifice, with a lateral one less distinct, which in 
A. parvula and A. Thompsoni is continued forward till it unites 
with the terminal one, the circular outline of which is interrupted 
at the point of junction. A small species, parasitic on A. divari¬ 
cata , shows the transition in the laterals exactly as A. prolifera 
does in the mesial sarcothecse. The laterals in A. superba and 
A. ascidioides are provided with two sub-tubular orifices, in 
addition to which, the whole front of the sarcotheca is completely 
free, forming a wide aperture, extending even beneath the part of 
the margin which bears the tubular ones. A. prolifera is 
similarly formed, except that in the laterals there is only one 
tubular aperture instead of two ; but in the cauline sarcothecse of 
this species as many as three of these sub-tubular orifices are 
found bordering the free margin. In forms like these the wide 
