$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 Polyj) a 

 kind of cupel, in the cavity of which the vitellus rests by a s-mall 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 Hijdra 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 apes 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-poIyi)s, gemmation always pre- 

 cedes propagation by eggs. 



2 Tlie eggs ot Hydra were long ago observed by 

 Bernhard Jussieu (Abliandl. d. schwed. Akad. 

 17i6, Vni. p. 211). But afterwards they were 

 regarded a? exanth;mata of this animal (see Roe- 

 sel, Insektenbelust. Th. III. p. £00, Taf. LXXXIII. 

 fig. 1, 2). Their true nature was lately first 

 pointed out by Ehrenberg (Abhandl. d. Berliner 

 Akad. 1836, p. 116, Taf. II.). 



3 The testicles of Hydra were known to the elder 

 naturalists, l>ut were taken for an eruptive disease 

 {Tremble.y Abhandl. zur Geschicht. eiuer Polype- 

 nart, p. 264, Taf. X. fis. 4, and Boesel, loc. cit. p. 

 502, Taf. LXXXIII. fig. i). Latterly this same 

 en'or 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 Verhaudl. d. Gesellsch. naturf. 

 Freunde in Berlin, 1S38, p. 14). 



i TFa^er, Icones zoot. Tab. XXXIV. fig. 10, 

 b, b. In Hydra vulgaris I have counted fifteen 

 testicles ; another mdividual 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 f^an Beneden (Rech. sur I'embryog. d Tubul. 

 pi. V. VI.), Rathk^ {IVie^mann's Axch. 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 capsules may be considered, being 

 sexless individuals Uke those mentioned in § 45, 

 in the category of nui-se-like generations which, af- 

 ter a more or less complete development, produce 

 generations with sex. 



* [At end of § 50.] 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 Z)a/(/tn!a and some of 

 the Rotatoria, all of which are properly gemmae, 

 and do not require the agency of the spermatic 



particles for theu- 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 pai-ent animal. This does not 



