bY K. J. TiLLYARt). 



407 



proiiymplial sheatli and the true larval head) is withdrawn, the 

 head oi the larva swells up greatly, and, by this means, the 

 pedicel of the egg is pushed aside, and the pronynij)!! emerges. 

 After a short period of time (from a few seconds to half-a-minute 

 at the most in Anax), the activity of the cephalic heart increases 

 rapidly, the head again swells up, but this time to almost twice 

 its previous size, and the larva escapes through the dorsal split- 

 ting of the pronymphal sheath. . 



Now there is no possil)le connection between the "head- 

 vesicle" and the interior of the embryo, except via the lai-val 

 mouth. If the cephalic heart be merely t^ temporary formation 

 in the ((esophagus, acting somewhat in the manner of a sucking- 

 pharynx, it would be able to exhaust all the liquid in the "head- 



Text-Hj^.3. — Head and poitiuii ut' thoiax nt' [jrunjiiiph ut' Ajia,i: jjajiHeiisi,-< 

 Buiiii., tu nhow, (a) (jouise of hlood-corpii-scles in tlit- head-rejfi(jii 

 (single arrows), and (h) suggested course of liquid Ijlood (lymph) 

 drawn into resophagus by action of cephalic heart (double arrows). 

 Diagrammatic. ( x 60) : aiif. antenna; da, d(jrsal aoita; e, eye 

 (dotted outline); It, larval liead; /ir, liead-vesicle; /c, larval cuticle; 

 /ill, labial mask; m, mouth; my, midgut; jji^ foreleg; ^>?-.v, pro- 

 iiymplial sheath; st, stomodteum or foregut. 



vesicle," by sucking it into the lumen of the oesophagus. Text- 

 fig.3 shows, in a diagrammatic manner, how this would be done. 

 The accumulation of all this volume of liquifl in the anterior part 

 of the oesophagus, together with the extra pressure caused by the 



