16 THE OCEANIC HYDROZOA. 



In Prai/a, the two nectocalyces are attached, nearly on the same level, to the proximal 

 end of the coenosarc. The inner surface of each is marked by a deep groove, and the smaller 

 is received within the bounding folds of the groove of the larger, so that the two form, 

 by their application, a sort of chamber or lii/drcecium, into which the coenosarc can be 

 retracted, as into a house. 



In the typical CalycophoridcB — Diphijes, and Abijla — a still further change has taken 

 place (PI. V). As in Prajja, there are but two perfect nectocalyces, but of these, one is 

 altogether on the distal side of the other, its pointed apex being received into a peculiar 

 cavity of the proximal nectocalyx, which takes the place of the internal groove in the 

 Phi/sophorida and Praya. It is to the summit of this cavity that the proximal, slightly 

 dilated end of the coenosarc, described above, is attached, its continuation, the somatocyst, 

 being imbedded in the substance of the nectocalyx. Proximally, therefore, the 

 hydrceciura in these Cali/cojjhoridw is entirely formed by the conical chamber of this 

 nectocalyx ; distally, it is continued by a groove, converted more or less completely into a 

 covered way, on the inner surface of the distal nectocalyx. The ca;nosarc, with its 

 appendages, travels up and down the complex hydroecium thus formed, and can sometimes 

 be completely retracted into it. 



The ducts which connect the nectocalycine canals with the somatic cavity come off, 

 as I have stated above, from the somewhat dilated, ciliated chamber in which the coenosarc 

 ends. The duct which goes to the canals of the proximal nectocalyx in Dijohi/es, runs 

 along that side of the hydroecium which is nearest to the nectosac, and divides into the 

 longitudinal nectocalycine canals close to the mouth of the latter. In Ahyla, on the 

 contraiy, it is extremely short, and divides directly opposite the middle of the nectosac. 



The duct which supplies the canals of the distal nectocalyx almost immediately enters 

 that beak-like process of the latter, which fits into the hydroecium of the pro.ximal necto- 

 calyx, and traversing it, divides into its four longitudinal nectocalycine canals, either 

 opposite the apex of the nectosac or close to it. 



I have described above the general arrangement of the four canals in the necto- 

 calyces, which radiate from the end of the communicating duct. Whatever the form 

 of the nectocalyx, that pair of these canals which occupies the median plane remains 

 straight, or as nearly so as the form of the organ will permit ; but the two lateral ones not 

 uncommonly undergo a curious flexure, of which a marked example may be seen in Plnjsopliorci}- 

 (see the description of that genus, infra). Leuckart describes, in the nectocalyces of 

 Hippopodius, Praya, Ilalistemma, and Agalma (and I can testify to their existence in the last- 

 named genus), what he terms " mantelgefasse." These are two slender, curved, csecal 

 diverticula, which are given off on opposite sides of the duct, shortly after it enters the 

 substance of the calyx, and lie in the same plane as the median nectocalycine canals. 



7. Beproductive Organs. 



These consist, throughout the Hydrozoa, of spermaria and ovaria, portions of the tissue of 

 the wall of the hydrosoma, and, I believe, more particularly of the ectoderm, metamorphosed 



' Also, according to Leuckart, in Agalma, Halistemma, and Apolemia. 



