HYDROZOA CRASPEDOTA. 761 



to a larger number, e. g. 200 or more, as in Aequorea. They are variously 

 branched in some instances. The genital organs are usually confined to 

 the radial canals but may extend to the manubrium, or be divided, one 

 part lying at the base of the manubrium, the other on the radial canals, as 

 in the Octorchidae. They appear as simple radial bands, divided sometimes 

 into two parts when radial muscles are present in the subumbrella. If long 

 they may be thrown into hollow folds, if short take the form of dependent 

 pouches. The tentacles are usually tubular with bulbous basis, in number 

 2, 4, 8, 1 6, or several hundreds. Other marginal appendages are (i) 

 marginal cirri present in a few genera of all the families, solid filaments 

 scattered between the tentacles, spirally coiled at their extremities, with 

 swollen ends armed with cnidoblasts : (2) marginal bulbs occurring only in 

 the ocellate families and in certain genera, short, thin, with bulbous ends, 

 provided, at least in some cases, with sense hairs : (3) marginal Mercies 

 present in some vesiculate genera, more or less conical eminences tipped 

 with cnidoblasts, usually black, and containing an evagination of the 

 circumferential canal, and frequently opposite to (4) the marginal funnels 

 or subumbrellar papillae which, unlike the preceding, are placed at the base 

 of the velum to the inner or subumbrellar aspect of the circumferential 

 canal. These papillae are conical, hollow, with a terminal pore, and their 

 lining endoderm cells are filled with brown granules and concretions. They 

 are without doubt excretory organs. Ocelli are found in the two families 

 Thanmantidae and Cannotidae, seldom in the Eucopidae and Aequoridae, 

 usually on the outer aspect of the tentacle-bulbs, rarely on the marginal 

 cirri or bulbs, or on the bell-margin itself in great numbers, e. g. Orchistoma. 

 Otocysts are characteristic of the families Eucopidae and Aequoridae. They 

 lie at the base of the velum, projecting to its outer aspect. The Eucopidae 



are small in size, averaging ^^ in., some, however, such as Obelia, do not 

 exceed - in. The majority of Leptornedusae, however, range from - 



5 O 



in. and upwards. Some Aequoridae^ indeed, are the largest of all Craspe- 

 dota, e. g. Aequorea Forskalea reaches from 8 to nearly 16 inches. 



The Medusan eye consists of sense-cells with pigmented (black, brown, 

 violet, red) supporting cells, with basal ganglion cells connected to the 

 outer nerve-ring. A cuticular lens is sometimes present, . e. g. in Lizzia. 

 The otocyst is primitively a groove lined by the ectoderm cells of the 

 subumbrellar side of the velum; certain of these cells contain each a 

 single calcareous otolith, and others connected to the inner nerve ring 

 are converted into sense-cells. Such otocysts are found in Mitrocoma 

 Annae. But in other instances the groove is very deep and the ecto- 

 derm cells at its margins proliferate and meet, thus turning it into a 

 vesicle. 



The sexual zooid is very commonly degenerate, and Is always so in 



