472 



Div. 3, ARTICULATED AXIMALS. 



trachese, extending parallel to each other throughout the entire length of the body, 

 having, at intervals, points from whence numerous branches extend, and which corre- 

 spond with certain external orifices, or stigmata* [or, as they have been termed in a 

 previous passage, spiracles], for the entry of the air. All of them have two antennae, 

 and the head distinct. The nervous system of the majority of insects (those with six 

 feet) is generally composed of a brain, formed of two ganglions opposed to each other, 

 united at their base, and emitting eight pairs of nerves and two single nerves, and of 

 twelve ganglions t, all of which are in the inferior part of the body. The two anterior 

 are situated near the union of the head and thorax ; the second and two following are 

 appropriated to the three segments of which the thdrax is composed, and the remaining 

 ganglions belong to the abdomen, each ganglion emitting nerves to the organs of their 

 respective segments. The two nervous cords which form, by their reunion, the ganglions, 

 are tubular, and composed of two tunics, the exterior of which exhibits tracheae. A 

 medullary substance fills the central canal. The fine work of M. Herold upon the 

 anatomy of the caterpillar of the Great Garden White Butterfly, examined during its 

 growth, and until the period of its transformation into the pupa, proves that the nervous 

 system and the digestive organs undergo decided modifications, the nervous cords being 

 at fir^t longer and wider apart, which confirms the opinion of De Serres upon the origin 

 and developement of the nervous system. We have already, in the general observations 

 on the three classes of articulated-legged Articulata, stated the difi^erent sentiments of 

 physiologists upon the seat of the senses of hearing and smell ; we shall therefore 

 merely add, that, in respect to the former, the small nervous ganglions situated upon 

 the forehead, of which w'e have spoken, appear to confirm the opinion of those who, 

 like Scarpa, place this sense near the base of the antennae. In some Lepidoptera, I 

 have detected two small apertures near the eyes, which may perhaps be the auditory 

 channels. If, in many insects, especially those with filiform or setaceous and long an- 

 tennae, these organs are used as tactors, it appears difficult for us to account for their 

 extraordinary developement in certain families, and more particularly in males, if we 

 do not admit that they are actually the seat of the organ of smell. Probably, also, as 

 regards the taste, the palpi, in those cases where they are very dilated at the tip, take 



the liL-iirt, ur iLe ubiloniiitHl i)oriion of tliis nrgAii, ts divi> ed, iiiter- 

 Uftlly^ iiitu fi^lit clininbcni in tlic Cuckclnifer, si-pariited fmni each 

 Oilier by two cniivf rj^fiit valves, which pt-riiiit tlie binoil to be pio- 

 pelletj forwHrds, bui i-revi-iit its returnintf. The dcfiniiioii Ki^'C" by 

 thix iiaiurnlibl of the ilorstal vessel, vvlintever may be the interior coin- 

 position ul thix urgiiii. evidently proven that it is not a real heart : 

 moreover, his ubservMti4tiis do not <leterinine the nature ol tliis duid, 

 Dor how it it. directed into the oiher piria uf rhe body, lo cfFecl their 

 nutrition. [The still inort reeent observations of Cnrus, Bouerbunk, 

 ftnd some others, have made us >t)d better aeqiminted with the nature 

 Ol thin d<j(Kiil ve>S(.-l, null its unes, < unii rilling the views ot Ilcrold as to 

 the existence of a di-ciiled circulation in insectK, otthough it in uf a 

 nature very disstimilar to that of the higher aniniaU} 



• Tl'C number of the neifinnita ol the body of the Myrlapoda being 

 vnrialde. that of their itpiracles it so likewiAe, and exterids sometimes 

 lo more than twenty. In hexapod insects, it is ufien eiKhteeri,— nine 

 oil each side. This H, however, more the case with tlie larva than tlie 

 perfect insect. Caterpillars, and most other larvie, have a pair of spi- 

 racles ill the seKnienl which bears the tirst pair of feet. The second 

 and third st^fnieiit!* are deficient, because, as I presume, the develope- 

 ment of ^viu^'s npnn these segments renders the prt sence of spiracles 

 unnecessary. Each of the fourth atid seven followinif segments cx- 

 Aibits a pair ; but in the perltct Deettes, in addition to the two anterior 

 ■piraclcf. whicli are hidden in the cavity of the prothorax or corslet, 

 and whitMt have not been noticed, two others are to be perceived, situ- 

 ated betwciii the base uf the elytra and win^j-s, bciiiff thote of the 

 Arsothorax; but there are none to the metathorax, unless we consider 

 those of >he tirsl abdoman 1 se^finent as suiipleiMelirnrv to the thorHX, 

 reiving upon what take-i plaice in the pedunculaivd H vmeitn|iitra and 

 l>i|:lera, uhcre the^e two segments, together with the dcini-»cumeuC 



to which they belong, form p;»rt of the thorax. Thus, in geiicriu. all 

 hexapod insects have eight pairs of spiracles to the abdomen, the twi> 

 last being often obsolete. In the Loeu>ts and Dragon-flies, the sides 

 of the inesothurax exhibit a pair of spiracles {tr^mtt^rrt, M. Serres), 

 In these and some other insects with uncovered wings, (he two fir^t 

 ihorncic spiracles are placed above, between the pro- and niesu-thorax. 

 Kxeept ill Libelluia, tlii; true tliorax does not exhibit any other spira- 

 cles. 1 bay tlie true thorax, brcause, in some, the twn anterior abdo 

 minal spiracles are traiislerred to the thorax. The metatliorax of the 

 Peniatrimie and SiutelU ree exhibits, on its under side, a pair of spira- 

 cles. Ill tlie wi^gle^8 s))ectre insects [Fhasmidie], the mesothnrax 

 has none, but tlie metatliorax has two pairs. 



[We tlius see that Latreille wah perfectly aware that each of the 

 three thoracic segments was occasionally provided with spiracles t 

 and yet his theory, whiih has been noticed above (that the hind part 

 of the thorax of the petiolated Hymenoptera and Diptera is abdo- 

 minal), is founded u|)on the supposition that the metathorax cannot, 

 of itself, possess spiracles, and that consequently the spiracles which 

 we fee on the hind part of the thorax of those insects, must be those of 

 the anterior abdominal segment, transferred to the thorax. The common 

 Karw ig, as I have shown in a memoir upi»n the anatomy of that insect, 

 published in the 'J'rrnisiirtiitTis "J thr En tntnotuf^ivftl />arieti/, c\h\hiti 

 an instance in which the pro-, meso-. and metathorax, are respectively 

 furnished with a pair of spiracles. I have also entered fully into this 

 question in the H> menopterous portion of my introduction to the 

 modern clanisification of insects, with a view to prove the gentral uni* 

 fonidtv nf the structure of the Hymenoptera with sessile and pdio- 

 luted qbd>)mens } 



t Some lamellicorn Beetles, in the perfect slate, are exceptions. 



