384 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
GLOSSARY OF TECHNICAL TERMS USED IN THE HANDBOOK. 
Acrocyst, an external, sac-shaped receptacle which rests on the top of the gonangium of certain species, 
and within which the generative products pass through the later stages of development. 
Actinule, a peculiar hydranth-like body which is found in the female gonophores of many tubularian 
hydroids. After being expelled from the gonophore it leads a free life for a while, and then settles 
down, becomes attached by its aboral end, and grows into a new colony. 
Bell, the gelatinous mass which forms the greater part of a medusa and is often called the “umbrella.” 
Blastostyle, a stem-like structure from which gonophores grow. 
Ccenosarc, the living cellular tissue within the perisarc. It is composed of an outer layer called the 
ectoderm, an inner layer called the endoderm, separated by a structureless membrane called the 
mesogloea. 
Corbula, the pod-shaped receptacle for the gonangia in certain genera of the Plumularidse. 
Eye-speck or Eye-spot. See sense-bulb. 
Fascicled stem, a stem which appears to be compound, or composed of a number of simple stems or 
tubes closely aggregated and often twisted together. 
Gonangium, the chitinous receptacle for accommodation of the gonophores of the calypteroblastic 
hydroids. 
Gonophore, the reproductive “person” of the colony which produces the generative products. It is 
usually destitute of a mouth and tentacles. 
Gonosome, the assemblage of structures directly associated with sexual reproduction. It includes the 
gonophores, blastostyles, ovaries, gonangia, meduspe, etc. 
Hydranth, a nutritive “person” of a colony consisting ordinarily of a body containing a digestive cavity 
surmounted by a proboscis which terminates in the mouth and is surrounded by radially disposed 
tentacles. A hydroid “polyp.” 
Hydrocaulus, the supporting framework of the colony, including the stem, branches, pedicels, etc. 
Hydrocladium, the branches which bear the hydranths in the Plumularidx. 
Hydrophone, the collar-like expansion of the pedicel at the base of the hydranth of the Plalecidse. The 
expanded margin is often several times reduplicated. It is supposed to be a reduced hydrotheca. 
Hydrorhiza, the root-like structure by which the hydroid colony is attached to stones, shells, or other 
bodies. 
Hydrotheca, the chitinous receptacle into which the hydranths of the calypteroblastic hydroids retract. 
It is usually transparent, and consists of an expansion and extension of the perisarc of the pedicel. 
IAthocyst, a usually glassy appearing body placed on the margin of the medusa bell and containing 
refractive granules. It is supposed to be sensory in function and to be used as either an organ of 
orientation or of hearing. 
Manubrium, the proboscis of the medusa. 
Marsupium, or Marsupial chamber, an internal chamber found within the gonangium of the genus 
Diphasia, in which the generative products pass through the later changes in their development. 
Medusa, the free-swimming “jelly-fish” often given off from the hydroid colony. It usually bears, 
and serves to distribute, the generative products. A 1 ‘ sessile ’ ’ medusa is one that remains attached 
to the parent stem after the generative products are expelled. 
Nematocyst, a “nettling cell,” or “ urti eating cell,” consisting of an outer sac containing a barbed 
thread, which can be rapidly projected with such force as to penetrate the tissues of the prey or 
enemy and inject an irritant poison. 
Nematopliore, a chitinous receptacle for the defensive “person” or sarcostyle of the Plumularidx. It 
is much smaller than the hydrotheca, but bears the same relation to the sarcostyle that the hydro- 
theca does to the hydranth. 
Operculum, a movable lid or cover which closes the aperture of the hydrotheca in many calypteroblastic 
hydroids. It consists of one or several pieces which are raised when the hydranth is expanded 
and lowered when it is retracted. In many cases the gonangia are also provided with opercula. 
Otocyst. See Lithocyst. 
Otolith, a highly refractile granule, one or several of which are found hi the otocyst. 
