PORPITA. 119 



through it, to end in the walls of the large central polypite, and of all the little ones which arc 

 disposed around it. 



" Before this, however, they form a plexus on the lower face of the liver, in the membrane 

 which carries the polypes, but, to all appearance, without divisions or anastomoses, of which 

 no definite evidence was seen in Porpita, except that here and there a few canals arose 

 from a common, very short stalk. In the central polypite these pneumatic filaments end, 

 partly on the attached wall, partly on the lateral walls, in which latter position a strono- 

 magnifying glass even will show them as white wavy lines. In the smaller polypites 

 four to six, also undulating canals, pass in their walls (m den Wiinden derselben) as far 

 as buds are atttiched, and then, so far as I could make out, end blindly. 



" Though there may be no opening of the aeriferous apparatus of Porpita in this situation, 

 it is very evident elsewhere, if a proper method of preparation be pursued. If all the soft 

 parts be removed from the under surface of a Porpita, in fact, and if the convex surface be 

 then observed with a low magnifying power, there is observable in it, besides the rich 

 vascular network to be described immediately, whose trunks are arranged radially, many 

 oval openings disposed serially between the vascular trunks, the outermost of which are 

 largest, while the inner are smallest.* 



" If the soft parts are now entirely removed, it becomes obvious that each of these 

 apertures corresponds with a hole surrounded by a low, depressed wall on the upper lamella 

 of the pneumatocyst, so that it leads directly into an air chamber. In a middle-sized Porpita 

 I can count forty-five series of pneumatic foramina, and in each series nine to thirteen 

 stigmata, so that, inasmuch as there are twenty-two to twenty-three air chambers, each series 

 of stigmata cannot communicate with all the chambers. 



" The most stigmata are possessed by the outermost chamber (which has sometimes one 

 in every series) and the next to it. From thence their number rapidly diminishes, and the 

 innermost chamber of all, which has the form of a round cell, has only a single central — 

 sometimes smaller, sometimes larger — foramen, which lies, consequently, in the centre of the 

 pneumatocyst. The size of the outer apertures, is 0'04 — 0'05"' ; of the inner smallest ones, 



0'015"' — 0024'" The pneumatocyst of Porpita consists of the same 



homogeneous cartilage-like tissue that forms the skeleton of Velella, and there is no ground for 

 the assumption of authors, from Eschscholz downwards, that it is calcareous " (1. c, 

 pp. 57—59). 



Professor Kolliker then goes on to show that the soft parts consist of a thin superior, 

 and a thick inferior layer, united in the broad marginal limb. The upper layer is thin, 

 and perforated by apertures which correspond with the pneumatic foramina. The lower 

 layer, much thicker, incloses the liver and the renal organ, and gives attachment to the 

 appendages. The upper surface of the lower layer exhibits radiating folds and grooves, 

 which correspond with the elevations and interspaces of the lamellae of the inferior surface of 

 the pneumatocyst. The brown hepatic cells are lodged in this lower layer, and extend 

 over nearly the whole area covered by the pneumatocyst. 



The roof of the cavity of the great or central polypite exhibits, in the middle, eight 

 radially disposed, cleft-like depressions, each with a round opening at the bottom, and many 



' In fig. 3, pi. xii, however, the innermost foramina are the largest. 



