354 REPORT—1863. 
the zooid is destitute of all power of true or sexual generation, and has as its 
proper function the nutrition of the colony. The other group of zooids (f, 7) 
has nothing to do with the nutrition of the colony ; it has as its proper function 
true generation, and the zooids which compose it give origin to the generative 
elements—ova and spermatozoa, either directly or after having first developed 
a special sexual bud. For the whole assemblage of the former or nutritive 
zooids I propose the name of “ trophosome”™, while to the latter or generative 
zooids I shall give the name of “ gonosome’’t. Every hydroid, therefore, with 
whose life-history we are acquainted, consists essentially, with the solitary 
exception already alluded to, and which will be afterwards more particularly 
mentioned, of a trophosome destined for the preservation of the individual, 
and a gonosome for the perpetuation of the speciest. 
The proper nutritive zooids (fig. 1 a, 6; fig. 2 a) which constitute the 
essential part of the trophosome of the Hyprorpa have long been known, in 
common with the zooids of the Acrrvozoa, by the name of Polypes. It will 
be more convenient, however, to restrict this term to the Acrrnozoa, to which 
Reaumur, borrowing it from Aristotle, who used it for the cuttle-fishes, 
originally applied it; while we may employ the term “ polypite”’ as proposed 
by Huxley§ for the alimentary zooids of the Hyprozoa. 
The polypite consists essentially of a digestive sac, opening at one end by 
a mouth, and prolonged at the opposite into a simple or branched tube 
which is common to all the zooids of the colony. Behind the mouth are 
situated, in almost every instance, tubular offsets from the digestive sac. 
These are known as “ tentacula”’; they are usually arranged in a single ver- 
ticil (Campanularia, Sertularia, &c.), sometimes in two, one behind the other 
(Tubularia), while they are sometimes scattered over the body of the polype 
(Coryne, &c.), or are partly verticillate, partly scattered (Pennaria)||. 
we are indebted to Prof. Huxley, who, in defining the “ individual” as “ the total result of 
the development of a single ovum,” proposed to designate by the term zooid all more or 
less independent forms which may be included as elements in this total result. (See Huxley, 
Observations on Salpa, &e., in Phil. Trans. 1851; Lecture on Animal Individuality, 
Ann. Nat. Hist. June 1852 ; and his review of J. Miller's Researches on the Development 
of the Hchinodermata, in Ann. Nat. Hist. July 1851. See also Carpenter, Princ. Gen. and 
Comp. Physiology, 1851, p. 906, and Brit. and For. Med. Chir. Rey. for Jan. 1848 and 
Oct. 1849, where he clearly supports the same idea, using the expression “a generation” 
for all that intervenes between one act of true or sexual generation and another. 
The distinction between a “zooid” and an “ organ” is not always easy, and may indeed 
sometimes appear to be arbitrary. T believe, however, that we may regard as a zooid every 
portion of an animal which is not the immediate result of true sexual generation, and is 
yet capable of independent existence, as well as such portions which, though never attain- 
ing to independent existence, yet homologically represent independent forms. In this sense 
not only are the free medusiform buds of the Hyprorpa true zooids, but we must also re- 
gard as such the fixed polypites and those fixed gonophores which never attain a developed 
medusiform structure, as well as the simple generative sacs which are developed on the 
radiating canals of Obelia, Thaumantias, &e. (see p. 401). 
* Tpégw, to nourish, and copa, body. 
+ Dévos, offspring, and copa. 
+ The trophosome of the Hyprorpa admits of an easy comparison with that of the 
SipHONOPHORA; but among the zooids which are associated in the trophosome of the 
StpHonorHora there are, in the Calycophoride and many Physophorids, besides those 
constructed for the immediate reception from without of the nutritive material which con- 
stitutes the food of the colony, certain others which are destined for locomotion and pro- 
tection, and whose part in nutrition is accordingly subordinate to that of the former. 
§ The ‘ Oceanic Hydrozoa,’ published by the Ray Society, 1859. ; 
|| In the Calycophoridee and most Physophoridee the tentacles of the polypite are reduced 
to a single one arising from its base, while the polypites of the Velellidse and Physalidse are 
altogether deprived of tentacles, their place bemg here apparently taken by analogous fili- 
4 
an 
