MUSEUM OF COMPARATIVE ZOOLOGY. 187 
corbula are homologous to the developed mesial nematophores of hydrothecæ, 
while the corbula itself is a metamorphosed pinna. To that theory the corbula 
of A. bispinosa seems to point, but even in it there are some difficulties to be 
explained before the corbula can be looked upon as a modified pinna. In 
A, bispinosa that pinna which bears the ribs of the corbula must be regarded as 
bearing two rows of hydrothecæ side by side, a condition which is found in the 
normal pinna of no member of the genus Aglaophenia. That the structures 
which have been described as corbule in Pleurocarpa are modified branches,* 
there can be no doubt. It seems also certain that they are homologous to the 
gonosomes open or closed of the genus Aglaophenia. — Pleurocarpa has a corbula 
pinosa. It differs from this species, however, in 
nearest related to that of 4. bi 
possessing a terminal extension of the axis of the corbula, which bears pinna, 
and in the absence of hydrothecæ at the base of the ribs of the corbula. A 
minor characteristic of Pleurocarpa is found in the mesial nematophore, which 
is very long, being continued beyond the orifice of the hydrotheca. The nema- 
tophores on the ribs of the corbula of Plewrocarpa are longer and more tubular 
than those on the gonosome of any known Aglaophenia. If we look upon the 
corbula as a modified branch, and not a metamorphosed pinna, the morphology 
of the gonosome of Callicarpa becomes plain. The spike of Callicarpa can then 
be regarded as a modified branch, and as a corbula homologous to the corbula of 
Aglaophenia. If that is true, in the same way the distal extremities of the 
branches in Hippurella are also corbulze. 
The fact that the margin of the proximal hydrothecæ is not as deeply 
notched as that of the distal, and that the mesial nematophore of the former 
rises but little from the margin, while that of the latter extends far beyond the 
orifice, seems to indicate that the growth of the hydrothec on the pinnæ takes 
place proximally as regards the main stem. In other words, instead of growing 
at its distal end, it elongates at the proximal extremity, and the oldest formed 
hydrothecæ are always at the most distal end of the pinna. 
CTENOPHORA. 
Ocyro8 maculata, Rana. 
Specimens of O. maculata were taken by Mr. Agassiz off St. Vincent. From 
his drawings and notes, the following description has been compiled. 
Ocyroé, as it floats in the water, is well marked by the presence on the walls 
of the oral lappets of four large spots, which are very prominent. These 
characteristic structures are situated on the inner walls of the oral lappets, and 
are formed by a great development of muscular fibres, concentrated in four 
areas. Similar muscular fibres, or rows of cells, are found on the inner wall of 
the oral lappets of all Bolina-like Ctenophores, where they are more regularly 
* Forbes, Edw., Ann. and Mag. Nat. Hist., Dec. 1844. Forbes regarded these 
bodies in Plumularia cristata as branches. 
