96 MANUAL OF ZOOLOGY. 



very many of its members having been shown to be realhkthe 

 free generative buds of other Hydrozoa. As used here, itjlor- 

 responds to part of the Gymnophthalmate Medusa of Professor 

 E. Forbes, the Steganophthalmate Medusa of the same author 

 being now placed in the sub-class Lucernarida. 



The hydrosoma of one of the Discophora (= a Gymnoph- 

 thalmate Medusa) is composed of a single gelatinous bell-shaped 

 swimming organ, the " nectocalyx" or " disc," from the roof of 

 which a single polypite is suspended (fig. 20). The interior of 



Fig. 20. Morphology of Medusidae. a A Medusid (Thaumantlas] seen in profile, 

 showing the central polypite, the radiating and circular gonocalycine canals, the 

 marginal vesicles and tentacles, and the reproductive organs ; b The same viewed 

 from below. The dotted line indicates the margin of the velum. 



the nectocalyx is often called the " nectosac," and the term 

 " codonostoma" has been proposed to designate the open 

 mouth of the bell. The margin of the nectocalyx is produced 

 inwards to form a species of shelf, running round the margin 

 of the mouth of the bell, and termed the "veil" or " velum," 

 by the presence of which the nectocalyx is distinguished from 

 the somewhat similar "umbrella" of the Lucernarida. The 

 endodermal lining of the central polypite or " manubrium " 

 (sometimes called the "proboscis") is prolonged into four 

 radiating canals, which run to the periphery of the nectocalyx, 

 where they are connected by a circular canal which runs round 

 its circumference, the whole constituting the system of the 

 " nectocalycine canals " (formerly called the " chylaqueous 

 canals "). From the circumference of the nectocalyx depend 

 marginal tentacles, which are usually hollow processes, com- 

 posed of both ectoderm and endoderm, and in immediate 

 connection with the canal system. Also round the circumfer- 

 ence of the nectocalyx are disposed certain "marginal bodies," 

 of which two kinds may be distinguished. Of these the first 

 are termed "vesicles," and consist of rounded sacs lined by 

 epithelium, and containing one or more solid, motionless con- 



