298 Mr. Poulton's notes in 1886 



an excellent example of a " pleurecbolic " introvert, 

 " acrembolic" during introversion, very clearly de- 

 scribed and distinguished from the converse type of 

 introvert by Prof. E. Piay Lankester (' Encyclopaedia 

 Britannica,' article "Mollusca," p. 652). As far as 

 I am aware, all the introverts in insects belong to this 

 type. One result of this organisation is the extreme 

 delicacy of the rim in the introverted organ, for the 

 smallest injury causing a thickening or a slight adhesion 

 on any part of the margin will entirely prevent eversion. 

 And it is in this manner that the flagella usually become 

 functionless : they are not otherwise injured in them- 

 selves, but are merely permanently introverted, and 

 can easily be seen lying in the receptacle. 



The organ is everted by forcing blood into it, and 

 advantage was taken of this fact in obtaining the 

 material from which fig. 8 was drawn. A loose ligature 

 of silk was placed round the apex of the receptacle of a 

 larva, and when the flagellum was fully everted on 

 irritation the ligature was tightened, and the flagellum, 

 being full of blood, was incapable of introversion. 

 Another ligature was applied immediately below the 

 former, and the receptacle divided between the two, and 

 the flagellum was then drawn with the aid of a camera 

 lucida. The structure was then hardened in a warm 

 aqueous solution of mercuric chloride, and subsequently 

 in spirit, longitudinal sections being taken through the 

 apex imbedded after long soaking in melted paraffin. 

 The structure of the organ, as shown by the sections, 

 is represented in Plate X., fig. 9 x 188. The appa- 

 rently smooth cuticle is seen to be covered with 

 extremely minute spine-like processes. The cuticle 

 itself is, as usual, made up of a homogeneous, super- 

 ficial, and a finely lamellated deeper layer, of which the 

 former is alone continued into the processes. Neither 

 of these layers contain pigment in this part of the 

 larva, but the pink colour is entirely due to the 

 immediately subjacent hypodermis cells. These cells 

 possess a fusiform outline when seen from the surface, 

 while sections show them to be flattened and to overlap 

 in an imbricated manner. The pink pigment is darkest 

 round the margins of the cells, and especially at their 

 apices. Beneath the cells is a very delicate layer which 

 represents the "dermal" tissue in many other parts, 



