MUSEUM OF COMrARATIVE ZOOLOGY. 137 



corbula are homologous to the developed mesial nematophores of hydrothecae, 

 while the corbula itself is a metamorphosed pinna. To that theory the corbula 

 of A. hispinosa seems to point, but even in it there are some dithculties to be 

 explained before the corbula can be looked upon as a modified pinna. In 

 A. hispinosa that pinna which bears the ribs of the corbula must be regarded as 

 bearing two rows of hydrothecae side by side, a condition which is found in the 

 normal pinna of no member of the genus Acjlaojihenia. That the structures 

 which have been described as corbulse 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 

 nearest related to that of A. hispinosa. It differs from this species, however, in 

 possessing a terminal extension of the axis of the corbula, which bears pmna, 

 and in the absence of hydrothecae 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 Pleurocarpa 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 pirma, 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 Hipp^trella are also corbulje. 



The fact that the margin of the proximal hydrothecae 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 hydrotheca; on the pinnae 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 

 hydrothecae are always at the most distal end of the pinna. 



CTENOPHORA. 

 Ocjnroe maciilata, Bang. 



Specimens of 0. maculata were taken by Mr. Agassiz off St. Vincent. From 

 his drawings and notes, the following description has been compiled. 



Ocyroe, 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 regidarly 



* Forbes, Edw., Ann. and Mag. Nat. Hist., Dec. 1844. Forbes regarded these 

 bodies in Plumularia cristata as branches. 



