April 1, 1868.] 



HARDWICKE'S SCIENCE-GOSSIP. 



81 



also, that there exist lateral veins which open into 

 each segment of the dorsal vessel, although from 

 the absence of pulsation and colour in the blood, and 

 their great delicacy and translucence, they are easily 

 overlooked, or confounded with other structures. 

 In its course through the body, the blood is brought 

 into close relation with the tracheal system, and 

 recent observations support the view that the blood 

 not only bathes the exterior of the air-tubes, " but 

 moves through that space between the outer and 

 inner membranes in which the spiral filament is 

 enclosed." 



In the Corethra larva the dorsal 

 vessel is a well-marked contractile 

 organ, the walls remarkably delicate, 

 so as to remind us of the same struc- 

 ture in the annelids rather than insects, 

 and the valves, although apparently 

 efficient, not so well defined as in some 

 species (fig. 50, m, and 57, a). It is 

 broadest near the tail, contracting a 

 little in the thorax, and near the head 

 divides into several branches. One of 

 these runs backward along the upper 

 side of the spinal cord; and accom- 

 panying the nerves given off from the 

 centre of each gunglion, I think I could 

 make out a slender branch running 

 to the dorsal vessel. The structure 

 may be compared to what is seen in the 

 small water leech (Glossiphonia biocu- 

 lata), where there is a capacious pulsating dorsal 

 vessel, joining laterally very slender non-pulsating 

 brandies, which look more like threads of con- 

 nective tissue than veins. As space will not allow 

 me to enter into details respecting the nervous 

 system, it will be better to note here, that on each 

 side of the dorsal vessel — at least in the ten ab- 

 dominal segments — we find ovate gunglionic bodies 

 (fig. 57, b), evidently attached by filaments to the 

 dorsal vessel, since they move up and down with its 

 contractions and dilatations. These gunglia also 

 anastomose with the nervous branches derived from 

 the cord. 



The circulatory system of insects is very simple, 

 for as the nutritive fluids of the body are freely 

 supplied with oxygen by the-air tubes, no compli- 

 cated apparatus is required. 



Digestive System. — I have already described the 

 formidable array of jaws and lancets designed for 

 the piercing and seizing of prey ; we may next 

 notice the apparatus for the digestion of food. Eirst, 

 in the thoracic region we find the oesophagus, which 

 is narrow when empty, but capable of considerable 

 distention (fig. 50, d). Its walls are thin, and com- 

 posed of three layers : externally, an epithelial layer, 

 easily detached and broken up ; next, the muscular 

 layer, with fibres running longitudinally and trans- 

 versely ; in the lower portion, oblique fibres are 



also visible, which decussate along the medial line. 

 The lining membrane is delicate, and near the crop 

 we observe the surface thinly covered with points 

 like crystals. At the lower end the oesophagus con- 

 tracts, and communicates with a curious compressed 

 gizzard (fig. 5G), formed of two valves, like the shell 

 of a Navicula, and in like manner marked trans- 

 versely with raised parallel lines . These r ugae are not 

 affected by liquor potassse, but it seems strange that 

 an animal which subsists on the blood and juices of 

 other species should require so powerful a crushing 

 apparatus ! A very narrow canal connects this 



Fig. 57. Posterior segments, x 16 diam. a. Dorsal vessel. The dotted 

 lines indicatethe course of the ventral and transverse veins, returning 

 blood to the dorsal vessel, b. Ganglionic bodies connected with it. 

 c. Posterior air-cells, d. Superior fascicle of hairs, e. Four bronchial 

 processes. /. Anal hooks, g. Anal tin. /*. Nervous cord. Above 

 which the four biliary ducts are seen entering the intestines. 



organ with the proper digestive cavity, or stomach 

 (fig. 50, /), which is readily distinguished by its 

 brownish colour, derived from the large secreting 

 cells which line the inner surface. Its direction is 

 serpentine, the chief flexure pointing downwards ; 

 opposite the eighth segment it contracts into a 

 narrow small intestine, and at the same point is 

 joined by four filiform biliary ducts. Lastly, we arrive 

 at an oblong colon, which terminates in a short 

 rectum, closed by sphincters (fig. 57, h). 



I could have wished to say something about the 

 nervous and muscular systems, both of which pre- 

 sent many points of interest ; and from the trans- 

 parency of the tissues, and the absence of the fatty 

 layer usually present in larvae, are displayed much 

 more clearly than is usual. But I have already 

 trespassed too long upon your patience, and can 

 only express a hope that others may be prevailed 

 upon to investigate the subject, and complete the 

 cycle of development, one phase of which I have 

 attempted to paint. 



Hedgehog. — In the Gironde vipers abound, and 

 the hedgehog is the declared enemy of the reptile. 

 Since so many hedgehogs have been destroyed, 

 vipers have increased at a fearful rate. — Land and 

 Water. 



