$ 50. THE POLYPI. 55 
same individual during the time of heat both ovaries and testicles are de- 
veloped upon the external surface of the body. 
In the place where the eggs are to appear,” the transparent and _color- 
less skin rises in the form of swellings, under which the vitelline mass 
gradually forms. These end each in the form of an excrescence, which,. 
being constricted at its base and rounded, has the shape of an egg. At 
the point of constriction there is formed from the body of the Polyp a. 
kind of cupel, in the cavity of which the vitellus rests by a small portion. 
of its surface ; at this point the skin becomes thin, and ultimately appears. 
like an arachnoid membrane enveloping the egg. In this last neither a 
germinative vesicle nor dot has been discovered. Its separation is preceded 
by a thinning of its surrounding membrane, after which the vitellus is im- 
mediately clothed by a gelatinous substance. In Hydra vulgaris its whole 
circumference is covered by obtuse prolongations of this kind, which, after 
an increase in length, divide, each once or more, at their extremity, and so 
present a dentated appearance. 
The arachnoid membrane finally bursting, the detached egg becomes 
fixed to some body, whilst the gelatinous coat entirely disappears. This 
is equally true of Hydra viridis, with the exception that here the vitelline 
prolongations are very short and compact. 
In these same individuals testicles are developed also. Between the 
base of the tentacles and the place of the appearance of the egg, there 
are developed small conical prominences, on the apex of which is a papil- 
la. This has an orifice which leads into an internal cellular cavity. This 
is the real testicle, wherein are found spermatic particles composed of a 
body, or head, to which is attached a very movable tail. These particles 
easily escape through the orifice, and circulate in the water surrounding 
the Polyps filled with eggs. The number of these testicles in a single 
individual is not definite. * 
1 In the arm-polyps, gemmation always pre- 4 Wagner, Icones zoot. Tab. XXXIV. fig. 10, 
cedes propagation by eggs. : 
2 The eggs of Hydra were long ago observed by 
Bernhard Jussieu (Abhandl. d. schwed. Akad. 
1746, VIII. p. 211). But afterwards they were 
regarded as exanthemata of this animal (see Roe- 
sel, Insektenbelust. Th. ILI. p. 500, Taf. LX XXIII. 
fig. 1, 2). Their true nature was lately first 
pointed out by Ehrenberg (Abhandl. d. Berliner 
Akad. 1836, p. 116, Taf. IT.). 
8 The testicles of Hydra were known to the elder 
naturalists, but were:taken for an eruptive disease 
(Trembley Abhandl. zur Geschicht. einer Polype- 
nart, p. 264, Taf. X. fig. 4, and Roesel, loc. cit. p. 
602, Taf. LX XXIII. fig. 4). Latterly this same 
error has been continued (Laurent in Froriep’s 
neuen Notizen, 1842, No. 513, p. 104). To Ehren- 
berg is due the first description of their true nature 
(Mettheil. aus den Verhandl. d. Gesellsch. naturf. 
Freunde in Berlin, 1838, p. 14). 
* ‘At end of § 60.] The so-called ova, mentioned 
above in the text, may be justly questioned as be- 
ing true ova, for we know of no real ova which do 
not contain a germinative vesicle. Then, again, 
simple oval masses of cells as they are, they would 
exactly resemble the bud-like eggs of Aphides, and 
the “hibernating eggs” of Daphnia and some of 
the Rotatoria, all of which are properly gemmae, 
and do not require the agency of the spermatic 
b,b. In Hydra vulgaris I have counted fifteen 
testicles ; another individual had seven eggs and 
eleven testicles ; and a third, four eggs and twelve 
testicles. 
[Additional note to § 50-] Other examples of 
Anthozoa having external genital organs in the 
form of egg or sperm capsules have been observed 
by Van Beneden (Rech. sur l’embryog. d Tubul. 
pl. V. VIL.), Rathké (Wiegmann’s Arch. 1844, I. 
Taf. V.), and Sars (Faun. littoral. Norveg. p. 7, 
Tab. II.), with Hydractinia, Coryne and Podo- 
coryne. See also the facts collected by Frey and 
Leuckart (Beitr. &c. p. 28). These egg or 
sperm capsules may, moreover, be regarded as 
imperfect male or female individuals, and then the 
porters of these may be idered, being 
sexless individuals like those mentioned in § 45, 
in the category of nurse-like generations which, af- 
ter a more or less devel d 
generations with sex. 
1 P 
particles for their development. It is also worthy 
of remark, in this connection, that these ova sprout 
from the same part of the body in which eggs are 
developed. Thomson, however (Edinb. New 
Philos. Jour. 1847, p. 287), speaks. of having ob- 
served the granular mass contained within these 
so-called eggs divide and subdivide like a proper 
vitellus, and this while still within the capsule, and 
attached to the parent animal. This does not 
