44 SELECTED NOTES FROM 



Fig. 5. — Transverse section of Maple, natural size. The regular 

 cracking of the bark into six equal divisions is well seen. 



,, 6. — Segment of the same, magnified 25 diameters, p., Pith; 

 S.V., spiral vessels; m.r., medullary rays, forming the means 

 of communication between the central and outer portions ; 

 l.f. , liber fibres ; c.|j. , cortical parenchyma ; c. 6. , cellular 

 layer of the bark ; c./. , corky layer of the bark ; w.l, ring 

 of wood of the first year's growth ; iu.3, ditto of second year's 

 growth; e.p. , the outer layer of cells forming the cuticle or 

 epiderm. The lines show the direction of the sections re- 

 quired to illustrate the subject completely, ur. , Vertical 

 radial — i.e., in a line with the medullary rays ; v.t., vertical 

 tangental — i.e., across the medullary rays. 



,, 7. — Very small leaf of Mercurialis perewnis, natural size. 



8. — Sphseraphides in the same, magnified 100 diameters. 



jj 



Plate IV. 



Figures illustrating early stages of Culex pipiens. 



Fig. 1. — The Larva in the position, head downwards, usually assumed 

 by it. It is drawn from a mounted slide, and is somewhat 

 contracted by the preservative fluid. a., Antenna; r.t., 

 respiratory tube, closed at times by valves (two only of the 

 six are here well seen) ; v. , vent, four delicate sub-triangular 

 plates guard the aperture. 



The normal number of segments in an insect's body is 13. 

 It is necessary for descriptive anatomy, or indeed for any 

 right understanding of what is seen, to be able to count them. 



1. — The head; 2, 3, 4. — Pro- meso- and meta-thorax. 

 The remainder are the abdominal segments. The apparent 

 tail, r.t. , is thus proved not to be a tail at all, but is really a 

 pair of members united to bear between them two large 

 tracheae, with their appendages. 



,, 2, 3, and 4. — Three successive stages in the development of the 

 Fupa. 



t.r.l., in Figs. 2 and 3. — A pair of trachiferous thoracic 

 limbs. These may be seen in life to move occasionally. 



The fifth segment, or second abdominal, bears a remarkable 

 pencil of hairs. a.L, Anal limbs, arising, like those forming, 

 by their union, the respiratory tube in the larva, from the 

 penultimate segment. They are terminated, each, by one or 

 two fine tactile hairs, indicated by t.h., in Fig. 4. Indeed, all 

 the hairs are tactile, or answer to the whiskers of higher 

 animals. 



In Fig. 4, the pro-thoracic spiracle, and the various abdo- 

 minal spiracles of the imago are marked, as also the haltere, 

 h.; p.r.s., pro-thoracic spiracle ; a.s,, abdominal spiracles. 



