990 



INSECTA. 



heat. These curious facts tend much to con- 

 firm the opinion as to the chief origin of animal 

 heat, but for farther illustration of this interest- 

 ing subject we must refer our readers to the 

 article RESPIRATION. 



Organs of generation. These parts have 

 already been treated of to some extent in a 

 preceding article, (GENERATION, ORGANS OF,) 

 and the forms which they assume in different 

 orders, more particularly those of the male 

 organs, having in part been described, we 

 shall only briefly allude to them on the present 

 occasion, in consequence partly of the great 

 length to which this paper has already been ex- 

 tended, and partly that we shall necessarily 

 return to this subject, more especially with re- 

 ference to the functions of these parts, in de- 

 scribing that class of Articulata, which in every 

 respect are so closely related to insects, the 

 Myriapoda, to which we must refer. 



In our observations on the skeleton we have 

 shown that the terminal segments of the body 

 invariably form part of the external organs of 

 generation. The long ovipositor of the Chry- 

 sididte, composed of four distinct annuli, retrac- 

 tile within one another, and even within the 

 proper abdomen itself, are only the terminal 

 segments of the body, which is thus made to 

 consist of fewer, but proportionately larger 

 annuli than the abdomen of those in which so 

 many segments are not employed in the forma- 

 tion of the generative organs. A corresponding 

 structure is also seen in the Panorpidx, in 

 which the separate annuli, not retractile to so 

 great an extent as in the Chrysidida, but capa- 

 ble of being extended to as great a length, are 

 distinctly shown to form part of the abdomen, 

 while the corresponding parts in the male, the 

 terminal segments, are developed into a claw- 

 shaped prehensile organ. A similar modifica- 

 tion of structure exists in all other insects. In 

 some species one or more of these parts be- 

 comes atrophied, or is developed to a greater 

 extent than the others, and the result is that in 

 some instances we find long, exsertile, and appa- 

 rently new organs, while in others some parts, 

 even of the annuli themselves, appear to be ab- 

 sent. But the normal number is almost every 

 where present, either simply as terminal plates 

 of the abdomen, between which the proper ex- 

 cretory portion of the organs of generation is 

 concealed, or more highly developed, and form- 

 ing a separate sheath for that structure. 



In the male insect (fig. 437) the organs con- 

 sist of an external portion, the penis (h), or 

 *' organ of intromission," in which is inclosed 

 the termination of the ductus ejaculatorius, 

 which extends backwards, and is connected 

 with the vesiculte seminules (e} and vasa defe- 

 rentia, which are connected with the epididymis 

 and the proper testes (a). These parts are 

 found in a large number of insects, in some de- 

 veloped to a great extent, but in others almost 

 entirely atrophied. This is the order in which 

 the parts are met with when passing from 

 without inwards. 



The penis of the male, like the ovipositor of the 

 female, assumes a variety of forms. It is usu- 

 ally inclosed between two lateral plates, the ana- 



Male organs' of generation 

 *of Athalia centifolice. 

 . (^ize Essay.) 



Fig. 437. Jogues of the sheath 



of the ovipositor, and 

 which are derived 

 from the terminal or 

 penultimate segment 

 of the body. With- 

 in this is a corrugated 

 soft membrane, the 

 preputium, which is 

 continuous with, and 

 is reflected inwards 

 from the inferior 

 margin of the anal 

 aperture, and sepa- 

 rates the organs of 

 generation from the 

 alimentary canal. 

 When the penis is 

 retracted it is covered 

 by this membrane, 

 which is corrugated 

 upon it (fig. 402, s). 

 In Coleoptera, as in 

 the Carabidte and 

 Melolonthida, the 

 penis is a long hor- 

 ny tube, retractile 

 within the abdomen on the under surface as far 

 as the anterior segments. The strong horny co- 

 vering of this organ is simply a consolidated state 

 of parts of the tissues which in other instances 

 are soft and flexible. It contains within it the 

 excretory portion of the ejaculatory duct. In 

 most of the Coleoptera, and in many other 

 Species, it has this strong hardened exterior, ne- 

 cessary apparently for its employment by cer- 

 tain species, in which there is little flexibility 

 of the abdominal segments, as an organ of in- 

 tromission. In Carabus monilis, as noticed 

 also in C. clathratus by Burmeister, the hard- 

 ened case of the penis is gently curved down- 

 wards to facilitate its introduction into the vulva 

 of the female. At its extremity on the under 

 surface it is a little elongated, and it is termi- 

 nated by a soft corrugated glandiform structure, 

 which is perforated in its centre, and represents 

 a glans penis, the perforation in its centre being 

 the orifice of the excretory duct. In other 

 Coleoptera the penis is also inclosed in a horny 

 sheath, and presents a great variety of forms in 

 different species. In many instances it is fur- 

 nished at its extremity with short hooked spines, 

 by means of which the male effectually retains 

 his connexion with the female. The external 

 sheath of the male organs, which incloses the 

 penis, is analogous to that of the ovipositor of 

 the female, and is employed when it is well 

 developed to open the vulva of the female. In 

 many species it is scarcely at all developed, 

 being like the sheath of the ovipositor only a 

 highly developed portion of the lateral plates of 

 the terminal abdominal segments. The cir- 

 cumstances above referred to will not allow us 

 to describe in detail the forms of these organs 

 of generation in many species, we shall there- 

 fore content ourselves with a brief notice of 

 some of those of the Hymenoptera (Jig. 437). 

 The general form of the penis in this Order is 

 similar to that of Athalia, and consists of a 



