REPORT ON THE TETRACTINELLIDA. 
117 
dimensions among themselves and from Eidley’s type. The anatrisenes are all longer 
than in Eidley’s specimens, and were it not that they form a graduated series I should be 
disposed to eliminate the specimen from Station 208, and make a distinct variety of it. 
The cladomes of the anatriaenes also differ somewhat in form as well as size, in some the 
length of the sagitta being less and in others more than half the length of the chord. 
Oxea. 
Dichotria;ne. 
AnatriiKne. 
Cladome of the Anatriaene. 
Length of 
Cladi. 
Sagitta. 
Chord. 
Station 186 (i.), . 
2-86 by 0-016 
2-825 bv 0-035 
2-65 by 0-02 
0-055 
0-04 
0-08 
)> )) d^-)j 
2-55 by 0-02 
3-034 by 0-03 
2-32 by 0-02 
0-071 
0-055 
0-096 
» » (iii-)j • 
3-42 by 0 0316 
3-42 by 0-047 
2-67 by 0-0175 
0-079 
0-072 
0-127 
„ 208, . 
2-79 by 0-024 
3-02 by 0-044 
3-02 by 0-024 
0-071 
0-048 
0-114 
Ridley, Report of the 1 
“Alert” Sponges, ( 
3 0 by 0-02.5 
3-0 by 0-035 
(0-022 
2-1 by < to 
(0-024 
The entire sponge varies from 7 to 11 mm. in horizontal diameter by 9 to 13 mm. in 
height. The ectosome (PI. XII. fig. 41) varies from about 0'3 to 0'5 mm. in thickness, 
and consists of collenchyme in which very small fusiform cells are present, as well as 
collencytes, becoming particularly numerous beneath the outer epithelium (PI. XII. fig. 
41). They are chiefly tangentially arranged, but some few radially. The tissue of the 
ectosome is reduced to a minimum owing to its extensive excavation by the subdermal 
cavities (PI. XII. fig. 39). These are traversed not only by the usual vertical spicular 
pillars and velar diaphragms, but also by horizontal partitions, which divide an outer 
smaller chamber in immediate communication with the pores from a larger inner chamber 
which is continued into an incurrent canal. The incurrent canals descend more or less 
radiately, taking a very irregular course, into the interior of the sponge. The oscule may 
be so small as to be invisible to the unaided eye, or it may attain a diameter of 2 mm. ; 
its size probably depending to some extent on the state of contraction of its margin. 
The margin is formed by a thin muscular membrane, about 0'08 mm. thick, which roofs 
over the cloaca. The cloaca (PI. XII. fig. 39) about 1 mm. deep by 0'725 mm. wide, has 
the form of a short cylindrical tube with a rounded base, its walls, about 0'3 mm. thick, 
or of the same thickness as the ectosome, consist of collenchyme ; they are traversed by 
numerous excurrent canals, which open freely on the free face of the cloacal wall, but are 
guarded by a strongly sphinctrate diaphragm at the level of the deeper face, where they 
enter the choanosome proper. The margin of the oscule is not fringed with spicules, but 
the walls of the cloaca are traversed by slender oxeas (4) which render its free surface 
finely hispid (PI. XII. fig. 39). The excurrent canals as they leave the cloaca and enter 
the sponge are provided at first with collenchymatous walls, and are crossed by velar 
