120 THE OCEANIC HYDROZOA. 



circumferential apertures, all of which communicate with the reticulated canals which 

 traverse the hepatic mass, and then pass into the radiating, branched, and anastomosing 

 canals, which traverse the inferior layer of the soft parts. Having reached the edge of 

 the pneumatocyst, they divide into two sets of branches, some of which pass into the 

 limb, while others ascend and ramify in the dorsal layer of the soft parts. All the larger 

 canals were ciliated. 



Kolliker alludes to the existence of peculiar gland-like organs, similar to those described 

 by Vogt in Velella, in the limb of Porpita. 



The canals of the peduncles of the smaller polypites or gonoblastidia open into the 

 hepatic canals, and the buds resemble those of Velella in their general structure. 



The canals of the tentacles are ciliated, at any rate in young specimens, and they 

 communicate with the vessels which proceed from the hepatic canals. 



Between the circumference of the central polypite and that of the liver there lies, 

 on the under surface of the body, a white lamella, perforated by many foramina, which gives 

 passage to the peduncles of the gonoblastidia and to the pneumatic filaments. It consists of 

 a reticulated tissue, sharply defined, and invested by a thin, fibrous membrane inferiorly, 

 while superiorly it runs into fine processes and trabcculjB, which pass between the hepatic 

 canals. 



The white colour of this plate arises from the presence of innumerable molecules, of 

 which the smallest look like spheroidal dots, and appear quite dark, while the larger 

 ones have the form of crystalline needles and rhombs, and are transparent, or are pale 

 and rounded, and have a more fatty and albuminous appearance. The chemical reactions 

 of the crystalline substance led Professor Kolliker to suppose it to be guanin, whence he 

 concludes that this organ has a renal function. 



With regard to the species of Porpita, Eschscholz admits the following : 



1. Porpita Mediterranea. 



The pneumatocyst is half as broad as the whole body, somewhat convex, and whitish on its 

 proximal or upper surface. The limb is dark blue, as in all the other species. The central poly- 

 pite and the inner gonoblastidia are whitish, the others becoming blue the nearer they are to the 

 edge. Tentacula bluish, and provided in their outer half with three series of tolerably long-stalked 

 capitula. The last capitulum of the lower series is sessile upon the point of the tentacle. 



This is the Holothiria denudata of Forskal, and the Porpita glandifera of Lamarck. It is 

 found in the Mediterranean, and attains a diameter of eight lines. 



2. Porpita ramifera. 



The pneumatocyst is convex at the sides, and flattened in the middle, and as convex 

 distally (or on its under surface) as proximally (or on its upper surface). The middle part is 



