DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 509 
§ Perivisceral Fluid and Corpuscles. 
The coelomic corpuscles of Annelids—particularly of the 
Oligochzta—have been so thoroughly investigated by Pro- 
fessor Kiikenthal (17), that I have found little to add to his 
excellent descriptions. 
Nevertheless there are some points connected with the 
numbers and condition of the corpuscles at different stages of 
development which are worth recording. 
The corpuscles themselves may be, as Kiikenthal has pointed 
out, of two kinds—(1) those with secreted granules, and (2) 
those without such granules. Both kinds are furnished with a 
nucleus. 
In the youngest stages (viz. A and B) only the small lym- 
phoid cells without granules are present; these cells are very 
darkly stained by borax carmine. Fig. 4 illustrates three such 
cells isolated by teasing up an embryo of stage B in glycerin, 
whose tissues had been fixed by osmic acid. These cells show 
every possible condition of amoeboid movement; in some cases, 
as shown in the figure referred to, they absolutely bristle with 
pseudopodia; at the other extreme are roundish or “ bipolar ” 
cells. It seemed to me that the intersegmental septa were the 
principal stations at which these cells originated, of course 
from the peritoneal layers covering the septa. 
In embryos of this age there was no fluid in the ccelomic 
cavities that could be recognised. In stage D the body-cavity 
was almost completely filled with granular corpuscles, which 
represent a further development of the small non-granular 
cells (see fig. 3). 
§ Larval Sense-organ. 
None of the embryos of Acanthodrilus showed any cilia- 
tion over the general body surface ; even the youngest embryo 
was apparently too far advanced in development to show any 
ciliation, with the exception of a patch at the anterior end, to 
which I shall refer immediately. As this embryo is older 
than a Lumbricus embryo in which the ventral ciliated 
