
No. 426.] THE CILIATED SPONGE LARVA. 457 
of these elements suggests that the sexual breeding season of 
the Hexactinellida, zf zt occurs annually, is one of very short 
duration. 
In the two species above alluded to, Leucopsacus orthodocus 
and Vitrollula fertile, Ijima has discovered not only archzeocyte 
masses but also larva, the only hexactinellidan larva as yet 
observed. Reserving for a later contribution his detailed 
observations on these bodies, Ijima contents himself for the 
present with a sketch of their structure and development. 
The larvae are spindle shaped, thicker at one end, and consist 
of a superficial flagellated layer covering an internal mass of 
cells. The hexactinellidan larva is thus fundamentally similar 
to that of monaxonid sponges. In an earlier stage the embryo 
is spherical in shape, with no discernible flagellation, and con- 
sists of a compact mass of small cells, those of the superficial 
layer showing an epithelium-like arrangement but not differing 
in general appearance from the internal cells. “Ata still earlier 
stage there is found a simple cellular mass agreeing in all 
respects with the latter" (the stage just described) “except in 
having no distinct epithelial covering. And that simple cel- 
lular mass is in all appearance nothing else than an advanced 
stage of what I have called the archzocyte congeries, of which 
there exists a series of different sizes, leading down uninter- 
ruptedly to the little groups of cells so commonly found on the 
chambers. At all events, there is nothing else than these 
compact groups of small cells to which the origin of the develop- 
ing embryo can be traced back with any degree of probability.” 
Ijima appreciates the remarkable character of the development 
just sketched and, before definitely formulating an opinion as 
to the asexual origin of the larva, wishes to continue his obser- 
vations on a more plentiful supply of material than he has 
hitherto had. His position is best stated in his own words : 
“To repeat, to me it seems certain that the embryo in a very 
early stage of its development consists of a small assemblage 
of uniform-looking cells, which differ in no distinguishable 
feature from the archeocytes. If the resulting body were 
something comparable to a bud or gemmula, I would probably 
have felt no hesitation in concluding that the cells were really 
