38 



THE LARVA OF THE BLOW- FLY 



distal joint (Figs. 4 and 5). The distal portion is sub- 

 hemispherical and has two short conical sensory papillae at its 

 extremity, one above the other ; it contains a pair of sensory 

 organs, which terminate in the papillae. These closely resemble 

 the eyes of a leech, except in being devoid of pigment ; they are 

 apparently sensitive to light (see Sensory organs). 



The proximal portion is sub-cylindrical, and exhibits a very 

 remarkable half-disc on its ventral and outer surface, the 

 stomal disc (mihi), and in front of the stomal disc the orifice 

 of a sac, in which the great hook lies when retracted. 



Yii^. 5. — a, the head and mouth of the adult larva of the Blow-Fly seen from the 

 ventral surface ; 3, Newport's segment ; 4, the prothoracic segment ; b, the 

 mouth more highly magnified {\ inch objective) ; /, the prestomal sclerite ; 

 d, the stomal disc ; w, aperture of the mouth ; //', the labium ; c, transverse sec- 

 tion of the pseudo-trachece of the stomal disc as seen with xV oil immersion lens. 



The real significance of these organs has been apparently 

 overlooked by Weismann and most subsequent writers, except 

 Macloskie* and perhaps Brauer [14, p. 32], who recognised that 

 the mouth parts of the larva correspond wath the proboscis of 

 the imago, without entering into details. This is more remark- 

 able, as the development of the maxillae is easil}^ traced from 

 the unmistakable maxillae of the embryo, from which they 

 scarcely differ, and these were correctly figured and described 

 by Weismann, who, however, entirely neglected the correspond- 



* See page 44. 



