1883. } The Siphonophores. 843 
bell cavities as.in Agalma and some other Physophoræ. The 
size of the swimming-bells of Gleba follow an opposite law of 
decrease in size from that which exists in Agalma. In Agalma 
the bells near the float are. very small, simple buds, while their 
size increases as we recede from that point. Those, however, 
which make up the most distant portion of the series are of 
about equal size. An opposite law exists in Gleba, for the swim- 
ming-bells near the end of the stem opposite that from which the 
polypites hang are the largest and those at the other extremity 
of diminutive size. By the arrangement of bells in Gleba those 
placed highest, as the animal naturally swims, are small, and 
those lowest are well developed, so that the axis is reversed as 
compared with that of Agalma. The polyp stem is inconspicu- 
ous or wholly wanting. The polypites and their appendages 
seem to hang from the upper end of the nectostem. The differ- 
ences between Gleba and Vogtia are mainly in the form of the 
nectocalyces, and by many the latter genus is regarded the young 
of the former. Much obscurity, however, still hangs about the 
anatomy and development of both these most interesting 
genera. : 
The following more or less artificial classification is presented 
as an aid to beginners in a study of these Siphonophora. The 
genera known from our waters are designated by an asterisk (*) : 
: SIPHONOPHORA. 
Polymorphic medusz generally with a tubular formed body. With or without a 
float. Young and adult free-swimming. With flask-shaped stomachs called poly- 
pites and long contractile tentacles. Many have swimming-bells, covering scales 
and tasters. Colonies moncecious or diccious. Reproduction (always) generally 
eggs. 
A.—With a float. 
Physophore. 
I.—Without axis, covering scales or nectocalyces. 
Physaliade.? 
* Physalia arethusa Til. 
II.—With an axis. 
a. Without covering scales or nectocalyces. 
Rhizophysidz. 
* Rhizophysa filiformis Forsk. 
* Rhizophysa gracilis F. 
* Rhizophysa eysenhardtii Geg. 
‘In a natural system of classification Physalia and Rhizophysa should be sepa- 
rated from the other Physophoræ, and form a new group of equal rank. For these 
Chun suggests the name Pneumatophoridæ (Pneumatophoræ). 
VOL, XVII.—NO, VIII, — 57 
