18 MEDUS.E OF THE WORLD. 



Pachycordyle and the Williadi, where it has become filled with a more or less solid core of 

 entoderm cells. The ring-canal is usually simple, and rarely gives rise to blindly-ending 

 diverticula. 



The proboscis, or manubrium, is usually flask-shaped, and the mouth in most of the 

 Codonidae is a simple round, or cruciform, opening, but in the Oceamdae it is surrounded by 

 lips which are more or less folded or crenated. Oral tentacles are found in the Margelmae, 

 and in some Cladonemidae. The stomach is often mounted upon a solid, conical peduncle, 

 but in Turritopsis the peduncle is made up of large, highly-vacuolated, entodermal cells which 

 constitute the walls of the proximal parts of the 4 radial-canals. The medusae are carnivorous, 

 feeding upon Crustacea, fishes, and other medusae or Siphonophorae. 



In the Codonidae the gonad encircles the manubrium in a ring-like manner, the mature 

 genital products being found in the ectoderm on the sides of the stomach. In the genus 

 Slabbena there are 2 or more of these genital rings. In the Oceamdae, however, the gonads 

 are restricted to the interradial, or adradial, sides of the stomach. Haeckel, 1879, believed 

 that they were radial in position, corresponding with the radial-canals, but VanhofFen, 1891, 

 showed that this was an error, for they are commonly interradial, or on both sides of each 

 radial line. In Eleutheria, according to Hartlaub, and possibly in other Cladonemidae, the 

 genital products are developed in the ectoderm of a peculiar brood-pouch, which is not 

 connected with the stomach, but is invaginated from the general ectodermal wall of the 

 subumbrella. In the Williadi and in Nemopsis the radial corners of the stomach extend 

 outward along the radial-canals, and the gonads develop upon the sides of these pouches. 

 Eleutheria is successively hermaphroditic, either sex preceding, but in all other Anthomedusae 

 the sexes are separate. The mature genital products are usually found in the ectoderm, 

 although they often originate in the entoderm. The eggs are cast out into the water by the 

 breaking down of the ectodermal walls ot the manubrium, but in some species of Bougatnvillia, 

 or in Margelopsis, or Hybocodon, the larvae may be retained until they have passed into the 

 planula or even into the actinula stage. None of the Anthomedusae are known to develop 

 directly from the egg into medusae, but the hydroid stages of many genera remain unknown. 

 Wherever the sexual development is known it is through hydroids of the Tubulanan order, in 

 which the medusae bud out separately and are not protected in special capsules or sporangia. 



Asexual development of medusae is found in Codonidae, in medusae of the genera Hv/>o- 

 codon, Slabberia, and Sarsia, and in the Oceanidae in the genera Cytieis, Dysmorphosa, Bou- 

 gainvillia, Rtithkea, and in the Williadi. In some of the Williadi the medusa-buds are borne 

 upon stolons which arise either from the radial corners of the stomach, or from the forks of 

 the radial-canals. In the case of Sarsia and Hybocodon the budding medusae develop as in 

 hydroids, the entoderm of the parent medusa forming the entoderm of the budded medusa, 

 and the ectoderm of the bud being formed from the ectoderm of the parent. In Rathkea, 

 Chun, 1895, discovered that the budding medusa is formed out of the ectoderm of the parent, 

 although a connection is finally established between the entoderm of the bud and that of the 

 parent a short time before the hud is set free. In Bougainvillia tuobe, on the other hand, 

 I find that the budding medusa is formed entirely from the ectoderm of the parent, no con- 

 nection being established between the entoderm of the bud and that of the parent. In the 

 genus Niobia the tentacle-bulbs develop into medusae and are set free. 



The majority of the Anthomedusae undergo a considerable development while swimming 

 freely in the water. In some cases, however, the medusae may, at times, become mature and 

 even discharge their genital products while still attached to the hydroid. This is seen in 

 Pennaria, Podocoryne, Sarsia, and Stylactis. Among the most short-lived medusae are those 

 of Pachycordyle, which have neither tentacles, marginal sense-organs, nor radial nor circular 

 canals. 



All of the Anthomedusae are inhabitants of salt water. They are rare in the open ocean 

 far from land, but are abundant along coasts, especially along continental shores, and many 

 of them thrive in harbors where the water may be more or less brackish. They appear to be 

 the simplest, and phylogenetically the oldest, of the Hydromedusae. 



