ORGANS OF GENERATION. 



409 



future observations to determine more accu- 

 rately the mode of reproduction in the corti- 

 ciferous polypes, which is a subject at present 

 involved in much contradiction and obscurity. 

 Taking this view of the subject, we find, 

 upon cursorily glancing over the ovigerous 

 classes of animals, that important modifications 

 of structure in the generative system render 

 further classification necessary, "in the lower 

 forms, ovigerous organs only have been dis- 

 covered, in which the ova are secreted, and 

 when matured, escape from the body, fit in 

 every respect for the production of a new 

 animal. In other instances, in addition to the 

 apparatus immediately appropriated to the de- 

 velopement of the ova, we find a superadded 

 portion destined to furnish a secretion which is 

 essential to their fertility, forming an apparatus 

 of impregnation. Sometimes the impregnating 

 organs are found in every individual, appended 

 to the ovigerous parts, rendering each creature 

 sufficient for the impregnation of its own ova : 

 in other instances, although each animal pos- 

 sesses both ovigerous and impregnating or- 

 gans, the cooperation of two individuals or more 

 is necessary to fertility; and in other cases 

 again, the apparatus which furnishes the ova, 

 and that destined to the production of the im- 

 pregnating fluid, are found in distinct indivi- 

 duals, distinguished by the appellations of 

 male and female: we shall accordingly di- 

 vide all oviparous animals into the following 

 groups : 



1. Such as are provided with ovigerous 

 organs only. 



2. Animals having, in addition to the ovige- 

 rous apparatus, a glandular structure, the 

 secretion of which is probably subservient to 

 the fertility of the ova. 



3. Ovigerous and impregnating organs, co- 

 existent in each individual, but the cooperation 

 of two or more needful for mutual impregna- 

 tion. 



4. The ovigerous and impregnating appa- 

 ratus existing in distinct individuals. 



FIRST DIVISION. Animals in which ovigerous 

 organs only have been distinctly recognized. 



It would seem from the observations of 

 Ehrenberg that some of the Polygastrica be- 

 long to this division, although the exact nature 

 of the generative system in such species remains 

 still a matter of uncertainty. In the Kolpoda 

 Cucullus the spawn consists of a loose mass 

 of ova, connected by delicate filaments, from 

 which the young are gradually evolved after 

 their extrusion from the parent animalcule, and 

 some of the parenchymatous Entozoa appear 

 to be similarly circumstanced. 



In the Acalephae, at least in such as have 

 been most attentively examined, the generative 

 system conforms to the type at present under 

 consideration. From the researches of Gaede 

 and Eysenhardt it appears that the ovaria are 

 four in number, disposed in a cruciform manner 

 upon the dorsal aspect of the body or that 

 which is opposite to the mouth. These ovaria, 

 which at certain seasons of the year are re- 

 markably distended and often beautifully 



VOL. ii. 



Coloured, open into the interior of the stomach. 

 The young Medusae are hatched in the ovaria, 

 and afterwards escaping into the alimentary 

 canals excavated in the substance of the body, 

 acquire in that situation a very perfect state 

 of development, and are ultimately excluded 

 through the oral aperture, or in the Rhizosto- 

 matous species through the ramified canals of 

 the pedicle. 



In the fleshy polypes (Actiniae) the ovigerous 

 system consists of long, convoluted filiform, 

 tubes, contained between the stomach and the 

 parietes of the body, and separated by partitions 

 which divide that space into compartments. 

 These tubes are attached by a delicate mesen- 

 tery, and according to Spix open in an irregular 

 manner into the digestive cavity, into which 

 the ova escape. The period or mode in which 

 the eggs are hatched is unknown, but that the 

 young escape fully formed and in every point 

 resembling their parent through the stomachal 

 orifice is attested both by Dicquemare and 

 Blainville.* 



The different forms of Echinodermata pre- 

 sent a similar simple arrangement of the gene- 

 rative apparatus. In the Asteriadae each ray 

 is furnished with two clusters of short ovigerous 

 tubes, which are closed at one extremity, but 

 open at the other into a cavity common to each 

 group. These organs open by a series of aper- 

 tures placed around the circumference of the 

 mouth at the base of each ray. In the spring 

 these ovaria are distended with eggs of a 

 reddish-brown colour, which are expelled in 

 clusters and left upon the beach exposed to 

 the influence of the sun, where they are ulti- 

 mately hatched .f 



The radiated type of structure is likewise 

 manifest in the disposition of the generative 

 organs of the Echinidse : in these the ovaria 

 are never single or simply bilobed, but are at 

 least four in number, or, as is generally the 

 case, five. Each ovigerous organ consists of 

 a simple dilated sacculus, which at certain 

 seasons is distended with ova, and at such 

 times in some species, as in the edible Echinus, 

 the eggs are sought after as an article of food. 

 The ovaria open externally by a corresponding 

 number of simple apertures, which are placed 

 around the anal orifice when it is central, but 

 otherwise are considerably removed from this 

 point. Nothing analogous to a male apparatus 

 has been detected in the Echinida. The eggs 

 are deposited in spring in the recesses of rocks 

 or among the fucus which covers them ; and 

 before they are hatched the young may be dis- 

 covered in the interior partially covered with a 

 calcareous shell, the rest of the integument 

 still remaining membranous. 



* Spix and Delle Chiaje assert that there are 

 other filiform tubes mixed up with the ovarian ducts, 

 which they regard as the testes, but neither the 

 observations of other authors nor our own exami- 

 nations confirm this view of the subject. 



t Tischer and Spix describe a singular flexuous 

 intestiniform organ which is found upon the dorsal 

 aspect of the stomach as a male apparatus, and 

 Blainville considers this part as in some degree 

 connected with generation. 



2 E 



