304 THE AMERICAN NATURALIST. [Vor. XXXV. 
hydrothece and gonangia. Sexual individuals when set free are known 
as Anthomeduse.  Medusz ocellate, z.e., the sensory bodies, are visual in 
character, and are located usually at the bases of the tentacles. Gonads 
borne in the tissues of the manubrium. 
IV. CAMPANULARLE (Calyptoblastea). 
Hydroids with hydrothece and gonangia. Colonial; propagating by 
budding both in development of hydrosome and in formation of gonosomes, 
the latter of which may become free as medusz, or only partially develop 
as medusoids, with only rudimentary medusan organs. Medusa with sen- 
sory organs of the vesiculate type, otocysts, borne upon the margin of the 
bell, usually between bases of tentacles. Gonads borne under the radial 
canals. Medusa when free are Leptomeduse. 
V. TRACHOMEDUSÆ. 
Hydromeduse devoid of hydrosome (hypogenic) medusa developing 
directly from the egg; no alternation of generations known. Sensory 
organs chiefly tentaculocysts, containing endodermal otoliths. Gonads 
borne under radial canals. Medusa generally somewhat hemispherical 
in shape, with thick mesoglea. Radial canals, four, six, or eight, often 
centripetal. 
VI. NARCOMEDUS/E. 
Hydromedusz devoid of hydrosome (hypogenic), development of medusa 
being direct with no alternation of generations. Medusa rather flat in 
shape, and with radial canals in form of broad gastric pouches, which vary 
in number, as do also the tentacles, which are usually set at some distance 
up on the outer surface of the umbrella. 
VIL SIPHONOPHORA. 
Hydromedusæ with free-swimming, polymorphic colonies, produced by 
differential budding. The colonies of this order are characterized by an 
extreme specialization of the several types of individuals which comprise 
them. Reproductive products borne in gonophores which seldom become 
ree. 
KEY TO FAMILIES OF TUBULARIÆ. 
Hydranth devoid of specialized receptacles, hydrothecæ. Sexual 
products not borne in closed gonangia. 
t. Hydranths with scattered, filiform tentacles . « .. CLAVE Re I 
2. Hydranths with single whorl of filiform tentacles : 
a. Hypostome conical, not abruptly differentiated. 
^. Colony regularly branched . . - . BOUGAINVILLIDA, 3 
