so 



HARDWICKE'S SCIENCE-GOSSIP. 



[April 1, 1868. 



an upper lip {labrum) (fig. 54, d). 5th. A pair of 

 strong four-toothed jaws {maxilla ?), (fig. 54, e), to 

 ■which are jointed smaller processes bearing brushes 

 of bristles (fig. 54,/). 6th. Two pairs of minute 

 palpi situated on each side the mentum {maxillary 

 and labial palpi ?) (fig. 54, g, h). [See Note, p. 78.] 



Fig. 54. 



Fig. 56. 



Fig. 54. Head, infero-lateral view. a. Antennae, b. Lancets 



(mandibulse). n. Palpi (leaf-like), d. Upper lip (labrum). 



e. Maxillae. /. Brush-like process jointed with them. 



g. Maxillary pulp. h. Labial pulp. 

 Fig. 55. One of the air-cells detached, a. Trumpet-like canal. 



b. Pigmentary cells scattered externally. 

 Fig. 56. Gizzard, and lower portion of oesophagus. 



fibril in the body. Now, in the larva of the Corethra, 

 the only traces of the longitudinal tracheae are the 

 four air-sacs I have already mentioned as occupying 

 the third and ninth segments of the body (fig. 50, b, c). 

 These are attached in pairs. Seen from above the 

 form is oval, and the surface irregularly reticulated 

 with black dots ; but when detached, or sub- 

 mitted to pressure under the microscope, 

 they are oblong and crescentic, and composed 

 of two coats, the outer smooth and tough, 

 the inner highly refractive, and surrounded 

 by a spiral fibre like ordinary tracheae {iig. 

 55). I have seen no trace of air-vessels con- 

 necting these sacs, but attached to one end 

 (and perhaps opening on the surface) is a 

 short funnel - shaped tube (fig. 55, «). 

 Whether capillary tracheae ai'e present, I 

 could not satisfy myself, but it is certain that 

 no conspicuous vessels exist. This is the 

 more curious because in the perfect insect the 

 tracheal system is said to be normal. Pro- 

 bably by watching the intermediate metamor- 

 phoses the difficulty may be explained.* 

 Some observers look upon the air-sacs as 

 mere floats, but I cannot agree with this 

 view. 



The black dots seen on the external surface 

 are round or oval pigment cells, irregularly 

 distributed on the upper side only. These 



are easily detached after death (fig. 55, a). 



The Eye (fig. 53) is large and black, and belongs to 

 the conglomerate type, as in the eyes of ento- 

 mostraca — i. e., formed of a number of simple button- 

 shaped lenses, imbedded in the pigmentary layer, 

 and having no special corner. Those on the outer 

 circle are free, and look like beads (fig. 53, b). 



Having taken up so much time with the de- 

 scription of the superficial parts, I must discuss 

 more briefly some points of interest respecting the 

 internal economy. All desire to learn the secrets 

 which nature hides so jealously— the circulation of 

 the blood, and the functions of assimilation and 

 reproduction ; and when we meet with an animal so 

 translucent that all the inner organs may be studied 

 under the microscope without the trouble of dis- 

 section, the mind must indeed be jaundiced that is 

 not stirred to wonder and admiration. 



Organs of Respiration.— Insects are air-breathing 

 animals, and the air is carried to their tissues 

 directly by vessels called trachea, kept open by 

 means of an elastic spiral fibre like the gas tubes so 

 much in use. There are usually two main longitudinal 

 trunks, from which branches proceed to the seg- 

 ments, and ultimately to every nerve and muscular 



The Circulation of insects is imperfect : in 

 part carried on by distinct vessels, and in 

 part through channels excavated in the tis- 

 sues. Its motive organ is the dorsal vessel ; 

 in fact, a compound heart, divided into seg- 

 ments by means of valves which allow the blood to 

 flow forward towards the head, but not to return 

 (fig. 57, a). 



There are other orifices opening laterally into 

 these segments, and also protected by valves, which 

 by many authorities are said to communicate directly 

 with the fluids of the body. But, as pointed out 

 many years ago by Mr. Newman, in his admirable 

 memoir on the Insecta {Encyclop. Anat. and P/iys.), 

 in some cases at least, the blood is returned to the 

 dorsal vessel by longitudinal veins, which collect and 

 carry it to the posterior chamber. It seems certain 



* Professor R. Jones thus describes the remarkably sudden 

 change following the assumption of the pupa state (I. c, 

 p. 103): " The air-sacs, situated both in the thoracic region 

 and in the hinder portion, burst and unfold themselves into 

 an elaborate tracheal system ; and a pair of ear-shaped tubes, 

 of which not the slightest trace could hitherto be discerned, 

 make their appearance upon the dorsal aspect of the thorax. 

 Two long tracheae seem to be thus simultaneously produced, 

 occupying the two sides of the body, and constituting the 

 main trunks, from which large branches are given off, to supply 

 iu front the head, the eyes, and the nascent limbs ; while 

 posteriorly they spread in rich profusion over the now con. 

 spicuous ovaries, and terminate by ramifying largely through 

 the thin lamellae that constitute the caudal appendages." 



