1. Simple tubes not branched, but more or less convoluted and closed at one extre mity.
2. Spiral tubes similarly closed, as in Spho drus tcrricola.
3. Spiral tubes rolled up into little balls, as in Carabus auratas, Aptinus displosor, Dyt iscus, &c.
4. Simple tubes irregularly branched, each branch vesicular near its extremity, as in Prionus roriarius.
5. Simple tubes, divided in a verticillate manner, each division being terminated by a capsule ; Scarabceus nasirornis, (Swammerdam.) 6. Simple tubes, divided as the last, but each division ending in a vesicle, as in Trichiusjitsciatas.
7. Simple tubes ending in stellated capsules, the apices of which are produced into slender tubes ; Ncpa cincrea, (Swam merdam.) 8. Simple tubes giving off a series of canals, each of which is terminated by a disc shaped capsule; Cetonia aurata.
9. Simple tubes, ending in flower-shaped capsules, i. e. each capsule consisting of a central vesicle, with other smaller ones placed around it, as in Asidagigas, (Edetnera calcarata, Diaperis violacea, Tenebrio obscures, (Edcmera cccrulea, &c.
10. Simple tubes, each terminated by a trans verse capsule, resembling the anther of a flower, as in Apis, Bontbyx, Scaris, Calviuia, &c.
11. Simple tubes, dividing into minute radia ting utricles ; Bostrichus capucinus.
12. Simple tubes, each terminated by a cap sule, which is covered externally with innumerable little vesicles or utricles, as in Mora asilus, Elater ,aurinus, Blaps gigas, Telephorasfuscus.
13. Simple tubes, ending in an elongated sac culus,to the sides of which are appended small vesicles arranged in longitudinal rows, as in &midis bicaudata.
14. Simple tubes terminating in vcrticillate utricles, as in Claus alreolarites.
15. Simple tubes, from which arise utricles arranged like the teeth of a comb, as in Hydrophilus pieeus.
16. Simple tubes, terminated by a simple sac culas ; Gyrinus natator.
17. Simple tubes, terminated by a bunch of vesicles.
18. Simple tubes, dividing into minute canals, forming a kind of cauda equina ; Th chodes apiarius.
19. Branched tubes, each branch being termi nated by a vesicle, as in Slaphilinas maxillosus. ( Fig. 202.) 20. Tubes very much branched, some of the ramusculi ending in bunches of leaf like utricles, others dilating into pe dunculated vesicles ; Sylpha obscura.
( Fig. 203.) 21. Simple loculated utricles, as in Ephe mera.
It is manifest from this sur vey that, although the secern ing organs differ so much in form, the canals composing them invariably terminate in blind extremities ; nor is it less obvious that the nature of the testis does not depend upon any peculiar arrange ment of the seminal tubes, but upon the increase of surface obtained by the various ar rangement of the vessels. Se cretion, therefore, here, as in every other case, is effected by the internal surface of tubes, utricles, sacculi, &c. the same end being accomplished in some eases by means of very lung simple canals, which in others is effected by smaller branches, tubes, or agglome rated vesicles.
Appended to the excretory ducts of the testi cular organs, near their termination, is found a group of ccecal tubes, evidently destined to provide an accessory secretion; these have been named from analogy vesiculce seminales. They vary much in their form, being sometimes elon gated, tortuous, convoluted, or ventricose, or at others short and straight. The seminal resides are generally two in number, even in those Lepi doptera in which the testis is single. In some insects, as Tenebrio nudityr and piecus, there are four; in others, as Dyliscus warginalis, six ; and in Lacusta and Vat ta, they are very numerous. In sonic insects these tubes are found to be of surprising length; thus in Oryctcs nasieornis they are twenty times as long as the body, and in Wotan aurata even sixty times the length of the animal. The vasa deferentia and vesicular seminales ulti mately terminate in one common tube, the ea nabs exeretorius, which communicates with the root of the penis; this canal is composed of muscular walls largely supplied with tracheal vessels, serving as a receptacle for the genital secretions, and no doubt is the agent by which, during coition, their expulsion is effected. The penis of insects is a hollow tube, capable of being protruded from the anal extremity of the body : its texture is generally membranous, but sometimes horny, and its shape exhibits considerable variety ; it is usually cylindrical or nearly so, becoming more slender towards its termination. In Chermis pyrus, however, the end is enlarged ; in the common wasp it is spoon-shaped; in Crabro bilobed, and in some rcsine curved and bifid at its extremity. In Musty: vivipara its apex is covered with spines ; in Tyrophaga entres and some other Muscid:c it is spiral. the penis of Coleoptera is furnished with a bivalve sheath, destined to open the vulva of the female prior to its inser tion. In some Diptem (1.11uscidw) a remark able inversion of the usual arrangement of the organs of copulation is observable ; in these the females are provided with a retractile penis, whilst in the males the generative apparatus terminates by a simple aperture. During coi tion in this case, it is the penis of the female which is introduced into the genital opening of the male, and thus becomes the recipient of the fecundating fluid. The Dragon-flies (Libel lula) are remarkable from the position which the male organ is found to occupy, being placed under the anterior part of the elongated abdo men, but in the female the sexual aperture occupies the usual situation near the anus. This arrangement accounts for the singular position which these insects assume during copulation.