SOFT PARTS AND MECHANISM OF THE PROBOSCIS. 403 



as such, although Leydig, and more recently Otto Rath [133], 

 recognised their nervous character. 



Each end-organ consists of a very thin capsule of flat cells, 

 loaded with dark-orange pigment granules. These cells are a 

 part of the hypoderm, which is also similarly pigmented in the 

 neighbourhood of the setae. Within the pigmented cells is a 

 layer of eight or ten fusiform nerve-cells, in which the nerve- 

 fibres terminate ; these enclose a single large cell, the tricho- 

 genic cell, which extends into the seta. The trichogenic cell 

 is clear and transparent, or possibly filled with fluid ; the 

 nucleus is pressed to one side of the cell by what appears to be 

 a large vacuole. The sheath of the nerve is continued as a 

 thin membrane between the pigmented sheath and the nervous 

 elements, and is apparently attached to the base of the seta. 



I am inclined to regard these organs as touch corpuscles. It 

 is possible, however, they may be special organs of taste. I 

 have sought in vain for organs of taste on the lips and ligula. 

 Kiinckel d'Herculais describes and figures such organs on the 

 ligula of Volucella, but I find no trace of any in the Blow-fly. 

 The only organs which appear to me to have the character of 

 organs of taste are on the maxillary palpi. The palpus receives 

 a very large branch from the labial nerve, and numerous gang- 

 lion cells exist in the interior of the organ, connected on the one 

 hand with the nerve-fibres, and on the other, by numerous 

 branches, with several layers of small cells which lie imme- 

 diately under the skin, and are most numerous towards the 

 extremity of the palpus. 



The setae on the palpus are of two kinds : large tactile setae, 

 few in number ; and small transparent setae, which are very 

 numerous. The large setae have similar organs to those con- 

 nected with the setae of the labial lobes. The small cells which 

 underlie the cuticle give off processes which enter the fine 

 setae ; and these are either grooved or hollow, and contain a 

 substance which stains deeply with carmine and logwood. In 

 this character they differ from all the other setae I have 

 examined. They appear to act as capillary tubes, which 

 become filled with the staining agent. It is well known that 



