178 PEOF. W. H. JACKSON ON THE 



rod. Together with a similar apparatus on the opposite side of the body, it serves to protrude 

 and retract the terminal papilla of the abdomen. Obj. aa, oc. 2, Zeiss, draw-tube in. The 

 figure is reduced J. 

 Fig. 20. Section of the elliptical chitinous body, e.b., guarding the entrance to the aperture of the duct 

 of the bursa copulatrix. It lies in a deep groove of the eighth sternum, and its centre is 

 occupied by a darkly stained mass of hypodermic cells, the cells forming a ridge in the pupa 

 and figured PL XIX. figs. 71, 72. The deeper or internal portion of the chitin forming 

 this body, and of the thickened part of the sternum, stains slightly with hematoxylin. The 

 soft tissues (hypodermis, &c.) have separated slightly from the chitinous cuticle of the 

 sternum, x , the line points to the spot where the bursal opening is situated in the next 

 section to the one here drawn. Compare fig. 25 of next Plate. Obj. B, oc. 2, Zeiss, draw- 

 tube in. 



Plate XVI. 



All the figures in this and succeeding Plates are taken from Vanessa Io, <j . 



Fig. 21. Lateral view of the abdomen of the caterpillar. 1-10, the segments of the abdomen. 3, 4, 5, 6, 

 and 10 carry prolegs ; 1-8 possess spiracles, indicated by the dark dots on each of them. It 

 may be noted that the series of large latero-dorsal spines is present on all the segments of the 

 abdomen, including the anal valve. The series of small spines immediately dorsal to the 

 spiracles is represented in the first segment by a tubercle with a small central hair-like spine. 

 A similar tubercle and spine are present on the ninth segment. The series of latero-ventral 

 spines ceases with the eighth segment. The line at the side indicates the natural length of 

 the specimen. 



Fig. 22. Lateral view of the abdomen taken from a specimen of a caterpillar which had just commenced 

 to throw off the larval cuticle ; the operation was completed by dissection. The metathoracic 

 wing has been cut away at its base ; the leg of the same segment has been left. 1-10, the 

 segments of the abdomen. The tubercles representing the large dorso-lateral larval spines are 

 confined to segments 2-7 ; in segments 6 and 7 they are deflexed by the stripping backwards 

 way of the larval cuticle. Spiracles are shown on segments 1-8, but the eighth is very 

 diminutive, s.r., sustentor ridge ; cr., cremaster. The natural length is indicated by a line 

 at the side. 



Fig. 23. Lateral view of the abdomen of a pupa 21 hours old, to show the remarkable contraction in 

 length and expansion in width which it undergoes, owing to the shortening of the muscles 

 and folding inwards of the intersegmental membranes. 1-10, the segments as before. The 

 first spiracle is completely hidden by the wings, the second and third partially. The eighth is 

 abortive. The line at the side indicates the natural length of the specimen. 



Fig. 21. Lateral view of the abdomen of an imago. 1-8, the terga of the corresponding segments ; 

 probably, however, the eighth terguin includes the ninth and what remains of the tenth. 

 The sterna of the first and second, and of the seventh and eighth segments are con- 

 tinuous ; but their separateness is indicated in both instances by ridges. Note a fold in the 

 last pleural membrane extending dors ally from the eighth sternum, which probably indicates 

 the posterior limit of the eighth pleural membrane. The pleural membranes are shaded by 

 diagonal lines. The terminal papilla of the abdomen is retracted as it always is in the natural 

 state of repose, but its hairs are visible. The line at the side indicates the natural length of 

 the specimen. 



The four preceding figures, 21-24, are all drawn to the same scale, — Obj. a*, oc. 2, Zeiss, draw- 

 tube in. They consequently show the changes in size which take place in the passage from the full- 

 jrrown larval to the imajnnal condition. 



