REPORT ON THE TETRACTINELLIDA. 
303 
tudinal canals, wliich run either within the ectosome, or immediately below it ; from 
these longitudinal canals, or sometimes without their intervention, but in direct continua- 
tion of the poral canals, others descend perpendicularly into the sponge, crossing the 
wall transversely, and traceable nearly as far as the oscular surface. The canals are 
crossed by vela, especially well marked near their origin. 
The ectosome (PL XXXIV. fig. 16) is about 0'24 mm. thick over the oscular and 
poral faces, but at the margin of the sponge it increases to 0'48 mm. in thickness. 
It consists of ordinary collenchyma; in places, however, especially adjacent to the canal 
walls, containing numerous oval vesicles, from 0’02 to 0'028 mm. in diameter, empty of 
contents, except for the presence of a small spherical nucleus, 0’004 mm. in diameter, 
inclosing a minute spherical nucleolus. By the coalescence of several such vesicles a 
cavernous collenchyma is produced here and there. Besides the branching collencytes, 
the collenchyma contains small fusiform cells with long tails like those described in 
Thrombus challengeri. 
The mesoderm of the choanosome is a sarcenchyma ; it contains numerous amoeboid 
cells irregularly dispersed through it, but most abundant near the ectosome. They stain 
more deeply with reagents than the surrounding tissue ; their average diameter is about 
0'03 to 0‘04 mm., and they present, embedded in their granular protoplasm, an oval 
nucleus, 0'0158 by 0'0118 mm. in diameter, within which is a very evident deeply 
stained spherical nucleolus, 0'005 mm. in diameter. 
The flagellated chambers are small, 0'0178 mm. long, by 0'0237 mm. broad; they 
are produced into a narrow aphodus which varies in diameter, measuring on an average 
about 0'0118 mm. 
The development of the desmas follows the usual course, the young forms occur most 
immerousl}?' near the inner surface of the ectosome and about the walls of the canals ; no 
clear evidence of a spicule cell was obtainable, though in two instances a flattened vesicle, 
containing a spherical granule and looking very like a nucleus with its nucleolus, was 
observed lying on the side of a young desma, the general surface of which was covered 
with a thin film of granular protoplasm. The nucleus, if it be such, measured 0’0158 
mm. in diameter, the nucleolus 0'004 mm. 
Corallistes masoni (Bowerbank) (PL XXXIV. figs. 1-13). 
Dactylocalyx masoni, Bowerbank, Proc. Zool. Soc. Bond., p. 91, pi. vi. figs. 1-4, 1869. 
„ „ Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xii. p. 437, 1873. 
Corallistes „ Zittel, Abbandl. d. k. baier. Akad. d. Wiss., Bd. i. p. 103, 1878. 
Sponge (PL XXXIV. fig. 1). — An irregular flabelliform or folded, sometimes proli- 
ferating plate, with a rounded sinuous margin ; erect, attached by an incrusting base. 
Surface smooth, even or dimpled. Oscules scattered on the inner face, situated on the 
