430 
MR. T. H. HUXLEY ON THE AFFINITIES OF THE MEDUSA. 
in the Annales des Sciences Naturelles for November 1845. This author has, as it 
appears to me, been misled by the great analogy between the structure of a Medusa 
and that of the generative organ of a Coryniform Polype, into taking the detached 
organ of the Polype for a real Medusa. He does not hesitate to say that the Clavi- 
form Polypes are “ only a first stage of development of the Acalephee.” He hints 
that each clavate Polype has its corresponding Acalephe, and he does not hesitate 
to give the latter distinct names as independent genera {Sthenyo, Cladonema). 
Here, as in many other instances, the study of the Diphydae throws light upon the 
matter. The detached free-swimming testis or ovary of a species of Sphenia has just 
as much claim to a distinct generic name as has Sthenyo or Cladonema, and yet in 
what respect does this differ from the persistent ovary of Eudoxia, which surely is an 
organ, and nothing but an organ ? 
Would it not be as reasonable to give a distinct name to Needham’s sperm-sacs 
because they exhibit certain independent motions external to the body of the Cepha- 
lopod ? 
The point is of consequence, because it is anything but desirable that true polypes 
with medusiform generative organs should be confounded with the Polypiform larvae 
of true Medusae. 
Description of the Plates. 
In all the sectional diagrams the letters have the same meaning, viz. m. Sto- 
mach. n. Common cavity, o. Canals, p. Generative organ, q. Natatorial organ. 
t. Tentacle, u. Marginal vesicle, x. Outer membrane, x'. Bract, x". Valvular 
membrane. 
PLATE XXXVII. 
Thaumantias ? 
Fig. 1. Disc seen from above. 
Fig. 1 a. Imaginary vertical section. 
Fig. 2. Opening of the stomach into the canals seen from above. 
Fig. 3. Marginal tentacles. 
Fig. 4. Young generative organ. 
Mesonema ? 
Fig. 5. Lateral view of the animal. 
Fig. 5 a. Vertical section. 
Fig. 6. View of a segment of the disc ; under surface. 
a. Buccal tentacles. 
h. Canals. 
c. Marginal membrane (20.). 
