^ 50. THE POLYPI. 55 



same individual during the time of heat both ovaries and testicles are dcv 

 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 p|-olongations 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 ann-polyps, gemmation always pre- 4 Warner, Icones zoot. Tab. XXXIV. fig. 10, 

 cedes propagation by eggs. b, b. In Hydra vulgaris I have counted fifteen 



2 The eggs of Hydra were long ago observed by testicles ; another individual had seven eggs and 

 Bernhard Jussieu (Abhandl. d. schwed. Akad. eleven testicles ; and a thii'd, four eggs and twelve 

 1746, VIII. p. 211). But afterwards they were testicles. 



regarded as exanthemata of this animal (see Roe- [Additional note to § 50.] Other examples of 



se/, Insektenbelust. Th. III. p. 500, Taf. LXXXIII. Anthozoa having e.xternal genital organs in the 



fig. 1, 2). Their true nature was lately first form of egg or sperm capsules have been observed 



pointed out by £Arcnfterg- (Abhandl. d. Berliner by Fare Beneden. (Rech, sm Tembryog. d Tubul. 



Akad. 1836, p. life, Taf. II.). pi. V. VI.), Rathki {fViegviann's Arch. 1844, I. 



3 The testicles of Hydra were known to the elder Taf. V.), and Sars (Favm. littoral. Norveg. p. 7, 

 naturalists, but were taken for an eruptive disease Tab. II.), with Hydractinia, Coryne and Podo- 

 {Trembley Abhandl. zur Geschieht, einer Polype- coryne. See also the facts collected by Frey and 

 nart, p. 264, Taf. X. fig. 4, and Roesel, loc. cit. p. Leuckart (Beitr. &c. p. 28). These egg or 

 602, Taf. LXXXIII. fig. 4). Latterly this same sperm capsules may, moreover, be regarded as 

 error has been continued {Laurent in Froriep''s imperfect male or female individuals, and then the 

 neuen Notizen, 1842, No. 513, p. 104). To Ehren- porters of these capsules may be considered, being 

 ierg- is due the first description of their true nature sexless individuals like those mentioned in § 45, 

 Olettheil. aus den Verhandl. d. Gesellsch. naturf. in the category of nurse-like generations which, af- 

 Treuude in Berlin, 1838, p. 14). ter a more or less complete development, produce 



generations with sex. 



* 'At end of § 50.] The so-called ova, mentioned particles for their development. It is also worthy 



above in the text, may be justly questioned as be- of remark, in this connection, that these ova sprout 



ing true ova, for we know of no real ova which do from the same part of the body in which eggs are 



not contain a germinative vesicle. Then, again, developed. Thomson, however (Edinb. New 



simple oval masses of cells as they are, they would Philos. .Jour. 1847, p. 287), speaks of having ob- 



exactly resemble the bud-Uke eggs of Aphides, and served the granular mass contained within these 



the " hibernating eggs " of DaoAreJO and some of so-called eggs divide and subdivide like a proper 



the Rotatoria, all of which are properly gemmae, vitellus, and this while still within the capsule, and 



and do not require the agency of the spermatic attached to the parent animal. This does not 



