PORPITA. 125 



away more towards the centre distally than proxiraally. They send prolongations down into the 

 lamellar folds or diverticula, which are directed still more obliquely, so that each diverticulum 

 is divided into a series of primary compartments (/"), whose axes are directed very obliquely 

 upwards and outwards when the animal is in its natural position. These primary com- 

 partments are divided and subdivided into secondary and tertiary compartments, which 

 become smaller and more numerous towards the free edge of the lamella, from which alone 

 the little groups of pneumatic filaments are given off. These filaments, similar to those 

 which arise from the central chamber, pass directly into the distal layer of the hydrosoma, 

 and sometimes at once go straight through it. The majority run obliquely, so as to 

 traverse the hydrosoma in all directions. Whether they anastomose or not, I cannot say; but 

 I liave never seen any clear instance of such an occurrence. Eventually, they seem to 

 pass out on to the distal surface of the hydrosoma, and there terminate in free ends, 

 those which are in the neighbourhood of the gonoblastidia at first twining about among the 

 gonocalyces. 



No pneumatic filament ever ends in the walls of the polypites, they are all on their walls, 

 and, so far as T have seen, no pneumatic filaments enter the tentacular area. 



The hydrosoma, or proper body of the Porjoifa, which incloses the pneuraatocyst, is 

 composed of a thin proximal, or dorsal layer, and a thick distal or ventral layer. In the 

 former, the anastomosing canals described by KoUiker are very beautifully displayed. It 

 in addition exhibits a number of comparatively large apertures, through which the tubercles 

 (/^) of the pneumatocyst pass. The hydrosoma, gradually thinning, rises for a short distance 

 upon the bases of these tubercles, and then can be traced no further, so that I have no 

 doubt the tubercles are naturally bare. Besides these apertures, there are a number of very 

 much smaller ones, not more than jj^th — ~oth of an inch in diameter, which coiTespond with 

 those urn-shaped tubercles which bear the pneumatic foramina. 



With regard to the inferior or distal layer of the hydrosoma, the only points I find 

 worth noting are the structure of the " tentacular area" and the distribution of the somatic 

 canals. As I have said, I find no pneumatic filaments traversing this region, or, at least, 

 passing out through it ; nor does the hepatic mass extend into it. The reticulated appearance 

 which it presents is due to the meshwork formed by a peculiar tissue, which consists of 

 l)ands ruiming perpendicularly from one face of the distal layer of the hydrosoma to the other, 

 and then spreading out and passing into the superficial substance. They resemble very 

 much, in fact, those fibrous bands which pass vertically through the substance of the dermis 

 in many fishes and BeptiHa, and tie together the successive layers of bundles of connective 

 tissue. 



The lamellfB of the proximal surface of the distal layer correspond with, and accurately 

 fit into, the intervals between the lamellar diverticula of the pneumatocyst. Tlieir proximal 

 edges are thin and sinuous, presenting shallow excavations, separated by sharp points. 

 They rise in height towards the circumference, and close to it, slope rapidly, so as to present 

 a convexity the opposite of that of the diverticula of the pneumatocyst. 



Each lamella has a wide sinus running along its proximal or dorsal edge, and com- 

 municating, by a series of more or less vertical channels, with the sinuses which lie in 

 the hepatic substance. 



These last appear to be disposed in several tiers, but the opacity of the mass renders it 



