MORPHOLOGY. 9 



Corynidce, Serlidariada [all?], Calycophoridce, Pliysoplioridce), or are produced into longer 

 or shorter folds or processes (many Medusidce, Lucernarian and other). 



I have above referred to the division of the polypite into a distal and a proximal portion 

 in many Ilijdrozoa. In the Calijcojjhorkke and F/iysojjIioridce, the polypite presents, in many 

 cases, a further division into a proximal (" basal- sti'ick" of the Germans), a median, and 

 a distal division. There is no distinct line of demarcation between the two latter, but 

 in many cases the median and basal divisions are very sharply separated, not only by their 

 texture, but by a distinct valve (PI. V). 



This, in the Calycophoiida, is a very well marked structure, though I do not find it noted 

 by any of those writers whose works I have consulted. It is a strong, circular fold of the 

 endoderm, whose lips, when the valve is shut, project into the cavity of the gastric, or median, 

 division of the polypite. As the oily or albuminous globules which result from the digestive 

 process are formed, they usually accumulate close to the valve, and are kept constantly 

 rotating by the cilia which line the gastric chamber. After remaining for a while in 

 this position, the fundus of the gastric chamber contracts, and forces the globule through the 

 valve, which appears to dilate at the same moment. The position and functions of this 

 apparatus, therefore, fully justify the appellation (A -a pyloric valve. 



The proximal division of the polypite usually takes on the form of a peduncle, which is 

 sometimes very long, and gives origin to various appendages. Its walls are ordinarily thin and 

 muscular, but the endoderm is sometimes much vacuolated, and partially obliterates its cavity. 



The median division of the polypite is the widest of the three, and has the thickest walls. 

 In it the process of digestion goes on, and hence it may with propriety be termed the gastric 

 division. The inner surface of the endoderm is richly ciliated, and not only is its general 

 thickness considerable, but in many CalycopJtoridce and Physophoridce it is developed into 

 larger or smaller, slender, conical, villous elevations. These villi are larger and more 

 distinct in Fhysalia (where they attain the length of Tsoth of an inch or more) than in 

 any other Hydrozoon I have examined (see the description of that genus, infra) ; but they are 

 very well developed in Athoryhia. In both genera they exhibit in their interior one or more 

 clear spaces or vacuoles, sometimes obscured by a quantity of dark pigment, and they 

 contain numerous thread-cells (Pis. IX, X). 



In Uliizophysa, Fhysophora, Diphyes, Ahyla, and other Calycophorida, the villi are 

 represented by shorter processes of the endoderm, which are sometimes obsolete, all that 

 remains of the villus being the characteristic clear vacuoles, imbedded in the endoderm, 

 and the production of the endoderm into ragged-looking filaments over them. 



Kolliker and Vogt describe similar organs in Hipjpopodim and Praya, so that such 

 short villi would seem to obtain universally among the Calycophorida. 



In the Jyalmopsls of Sars, in Jyalma, Forskalia, and Apjolemia, the villi take on the form 

 of longitudinal ridges, which usually contain much pigment, and thus give a very marked 

 character to the gastric division of the polypite. They have been confounded with reproduc- 

 tive organs. 



Gegenbaur (p. 23) describes the vacuoles in the villi of Praya maxima as cells. " The 

 contents of these cells differed greatly, sometimes appearing perfectly clear, at others 

 yellowish or brownish, and, in this case, frequently consisting of minute particles. The 

 colour then shines through the walls of the polypite. I corisider these to be hepatic cells, 



2 



