424 
MR. T. H. HUXLEY ON THE ANATOMY OF THE MEDUSiE.» 
openings of the sacs could be perceived ; the sacs were filled with spermatozoa with 
triangular heads, about YO^^th of an inch in diameter, and very long, fine, delicate 
tails, fig. 31 a. The course of their development appeared to be as in Phacello- 
phor'a, 
50. Rhizostoma and Phacellophora then agree in having the spermatozoa deve- 
loped in sacs connected with the inner “foundation membrane” and opening inter- 
nally. It would appear from this that the exit for the spermatozoa is through the 
mouth of the animals, though this course in Rhizostoma would certainly be a rather 
circuitous one. 
51. The individual of Cephea (C. ocellata) which I examined resembled, with 
regard to the generative organs, a young Rhizostoma. The line of generative tentacles 
was present, but the generative organs were undeveloped. According to Will, the 
structure of the testis in Cephea Wagneri closely resembles that of Rhizostoma. He 
says that there is a cavity under the disc into which the canals of the arms and disc 
open ; that the floor of this cavity is forined by a thin membrane covered with fine 
tentacular appendages, and that the band-like testes are attached to the under free 
surface of the membrane ; they consist of pyriform sacs {flaschenfonnigen Driischen) 
closely applied together, and each opening independently below. The spermatozoa 
are elongated and cylindrical, and have a very long, fine appendage. 
52. With regard to the muscular system of the Medusae, such observations as I 
have made lead me to believe that the muscular fibres are always developed in the 
outer “foundation membrane.” In Rhizostoma the muscular fibres of the under sur- 
face of the disc are flat, pale, and from to y^th of an inch in diameter. They 
run parallel to one another, but the lines of separation between them are not con- 
tinuous throughout, but thus : each fibre is made up of very small • 
and indistinct fibrils, which are transversely striated, the striation ~ 
being most distinct at the edge of the fibres. 
53. I have not observed any indubitable trace of a nervous system in the Medusae. 
54. Will has described a blood-vascular system, consisting of a system of canals 
inclosing the water canals and containing a distinct fluid with cells floating in it. I 
have paid particular attention to this point in all my examinations of the Medusae, 
but notwithstanding that I have had species of the very same genera {Cydippe, Cephea, 
Thaumantias) under my hands, I have never observed any trace of it. I am at a loss 
even to understand what he means, unless, as I strongly suspect, he has taken the 
outer foundation membrane, which occasionally is thick and distinct from the inner, 
especially about the circular marginal canal, for the walls of a distinct vessel. Even 
if this be the case, what are the blood-corpuscles ? 
55. The thread-cells resemble in all respects those of the Diphydge, which I have 
described elsewhere, consisting of a delicate outer cell inclosing another thick-walled 
cell, with a spiral filament of greater or less length, coiled up in its interior and 
capable of protrusion on pressure. 
