27 
Dr. Reid on the Development of the Medusse. 
numerous minute nuclei disseminated through it. Numerous 
nearly elliptical and oval capsules (filiferous capsules), having a 
long thread or filament coiled up in the interior of each, are fixed 
upon the outer surface of the external layer, and in much smaller 
number upon the inner surface of the internal layer, where it lines 
the internal cavity or stomach. These capsules are most abundant 
upon the external surface of the tentacula. Fig. 20 is a highly en- 
larged view of a small portion of one of the tentacula, showing 
the filiferous capsules attached to its outer surface. These fili- 
ferous capsules vary much in size, but the largest are generally of a 
uniform size, nearly of an elliptical form, and about 
inch in their largest diameter (PI. V. fig. 8). Several of these, de- 
tached in examining portions of the larva under the microscope, 
had burst open at the smaller end, and the spiral thread projected 
through the opening and was uncoiled (fig. 9). In the entire 
capsule a rounded and narrow column passes from the smaller end, 
beyond which it slightly projects, in the direction of its longest 
diameter, nearly to its other extremity ; and tliis column, to which 
the spiral thread is attached, protrudes from the interior of the 
capsule when it bursts. I have never observed these filaments 
projecting from the capsules when adhering to the surface of the 
body, unless when subjected to pressure, but it is difficult to use the 
more powerful object-glasses necessary for distinguishing these, 
without compressing more or less the part under examination. 
The internal is considerably thicker and more opake than the 
external layer, is of a slightly yellowish colour when it accumu- 
lates at any point in greater- abundance than usual, and is folded 
inwards to form the four equidistant projections seen on the sur- 
face of the stomach when the mouth is dilated (fig. 5 a), and 
when the body of the animal is slit open and then spread out 
(fig. 6 c). By making a transverse section of the body, the rela- 
tive thickness of the internal and external layers, and the man- 
ner in which the internal is folded to form the four pouches or 
short canals that project from the internal surface, are very di- 
stinctly seen (fig. 7). These four short canals (fig. 7 a) termi- 
nate at their upper end in another canal, encircling the mouth 
and placed between it and the margin of the dise (fig. 6 b). Into 
this circular canal the hollow tentacula also open. The inner 
surface of the circular canal and the tentacula is lined by the in- 
ternal layer. The four depressions (fig. 2 a) placed between the 
mouth and margin of the disc correspond to the termination of 
the four vertical in the circular canal. Across the bottom of 
these depressions, which at first sight look like apertures, a mem- 
brane is stretched sufficiently thin to permit readily of the trans- 
udation of fluids. 
x\fter reading Steenstrup^s observations on the structure of 
