118 THE OCEANIC HYDROZOA. 



any particular reason being assigned for the distinction ; the fact being that both have a 

 cartilaginous consistence, while neither is calcareous. He describes the radiating perpen- 

 dicular lamellae of the distal surface, and says that the flatness or more rounded character 

 of the body depends on the depth of these. 



The capitula of the tentacles are called suckers (saugniipfen), and are said to be 

 provided with longer or shorter pedicles. Does the following passage refer to the pneumatic 

 filaments or to the misunderstood peduncles of the gonoblastidia, or to both ? 



" Between the suckers one sees a great number of peculiar organs, which are probably 

 receptacles for germs (keini-behiilter). Mucous globules beset with white points are disposed 

 in alternating series along a fine median tube'' (1. c, p. 176). 



I find no addition of any importance to our knowledge of the organization of Porpita, 

 until the publication of Krohn's observations upon the pneumatic filaments cited above. 



Subsequently to the promulgation of his discoveries, Kolliker's important investigations, 

 which were first published in 1853 (' Bericht liber einige im Herbste, 1852, angestellte 

 Untersuchungen, Siebold and Kolliker's ' Zeitschrift,' 1853), have brought us much nearer to 

 an exhaustive knowledge of the organization of this animal. I partly translate and partly 

 condense his excellent memoir on Porpita, contained in 'Die Schwimmpolypen.' 



"As in Velella, the pneumatocyst (knorpel-platte) of Porpita is thickest at the edge, 

 thinnest in the middle, though, on the other] hand, each of the the air chambers, of which 

 the outermost are the widest, is, on account of the circular form of the organ, of even 

 diameter throughout. If they are filled with air, or in a fresh pneumatocyst (schale) still 

 containing its air, it is observable that the inner contour of each air chamber is a simple 

 circle, while the outer appears to be undulating; whence it follows that the septa have 

 tolerably regular, small projections on their inner surfaces. From these septa, also, the 

 elegant concentric striations, visible even with the naked eye, on the upper slightly convex 

 face of the pneumatocyst (knorpel-scheibe), arise, whilst the radial striation visible on both 

 faces, but especially on the under, results from linear elevations of the cartilaginous walls 

 which, upon the under side, are so pronounced that they may rightly be termed ridges or 

 lamellae (Leistea oder Blatter). 



" The relations of the air chambers of the pneumatocyst to the external parts are much 

 more interesting in Porpita than in Velella. The pneumatic filaments (luftcanale) discovered 

 by Krohn, and already mentioned in describing Velella, are present, and in much greater 

 numbers, as are also the pneumatic foramina, which have not as yet been noticed by any one. 

 The pneumatic filaments arise from the inferior concave surface of the pneumatocyst, 

 in as many series as there are radiating lamellae, and in fact in such a manner that every air 

 chamber, with the exception of the outermost, gives off one or many pneumatic filaments. 

 Since the number of chambers in a middle-sized Porpita (four or five lines in diameter) 

 is twenty-two or twenty-three, and that of the lamellae of their concave surface (of which, 

 however, many are very short, and only visible on the outer parts of the shell) is eighty or 

 ninety, it results that the number of the pneumatic filaments is out of all proportion to 

 that of the same organs in Velella. In other respects they are similar, only that they 

 have thinner walls and are narrower (O'OOS— 0015"'), and are not only provided with 

 internal projections, but also exhibit external prominences. After arising from the 

 pneumatocyst, they at once enter the liver, and pass in a wavy but tolerably direct course 



