CYSTONECTAE. 155 



madenia are confined to the under part of the pneumatocyst. The 

 float bears on its dorsal side a crest formed by a fold of the trunk, 

 i.e., of the part of the body which projects behind the sac (as well 

 as ventral to it), and which carries the cormidia. The pneumatpcyst 

 extends into the crest, and becomes divided up by a number 

 of transverse septa into air-chambers. The cormidia are very 

 numerous; they appear to be dissolved in the old individuals, but 

 in the younger stages they are ordinate. When they can be made 

 out they may be seen to consist of palpons, siphons, and branched 

 gonostyles arising from a common stem. The tentacles arise from 

 the palpons. The gonostyles are hermaphrodite, and the female 

 gonophores break away and develop their ova as free -swimming 

 Antliomedusae. 



The youngest larva of the Physalidae is known as a Cystonula. It has a 

 float and one siphon with tentacle hanging below it. Later it elongates 

 horizontally and produces on the ventral side, anterior to the first siphon 

 (i.e., nearer the morphological apex), the cormidia. The primary siphon or 

 cormidium persists at the hinder end of the float, i.e., at the end opposite to the 

 stigma, and is in some forms always marked off from the numerous secondary 

 cormidia. 



There are monogastric and polygastric forms in the order. The pneumatocyst 

 has generally a gas-secreting thick epithelium or pneumadenia in its basal part. 

 This may be partly constricted off as a hypocystic air-funnel. The epithelium 

 of the pneumadenia in many forms sends out branching villi of its ectoderm 

 which project into the pericystic space, and are covered towards the latter 

 by its ciliated endodermal lining. These hypocystic villi are composed of 

 large cells and are solid. They are probably mechanical in function helping 

 to support the air-vessel. 



In many forms the gonostyles bear palpons (gono-palpons) ; and in the 

 Physalidae the palpons have a tentacle. The tentacles are often branched, 

 but without a cnidosac (battery). The sting of Physalia is particularly 

 poisonous. 



Fam. 1. Cystalidae. Monogastric, with one large siphon bearing a tentacle 

 and surrounded by a corona of siphons. Pneumatophore without radial septa 

 or hypocystic villi. Cystalia H. 



Fam. 2. Rhizophysidae. Polygastric, with a long stem bearing in its 

 ventral median line numerous monogastric cormidia with single palpon and 

 tentacle. Pneumatophore large with radial pericystic pouches, but with hypo- 

 cystic villi. 



Sub-fam. 1. Cannophysidae. Cormidia ordinate. Gonostyles attached 

 to the stem at the base of the siphons. Aurophysa H. ; Cannophysa H. 



Sub-fam. 2. Linophysidae. Cormidia dissolved. Gonostyles attached 

 to stem between the siphons. Linophysa H. ; Nedophysa H. ; Pneumophysa 

 H. ; RMzophysa Per. and Les. 



Fam. 3. Salacidae. Polygastric with long stem bearing in its ventral 

 median line numerous polygastric cormidia. Pneumatophore large, without 

 radial pericystic pouches, but with hypocystic villi. Salacia H. 



