43 



but there are most usually uine of them. Out of eight 

 individuals which were specially examined Avith reference 

 to this organ, four of them had nine triangular bodies, 

 two had ten, and the remaining two possessed seven and 

 eight respectively. Both Laboulbene and Feriuild have 

 observed specimens which had seven to the organ on one 

 side of the head, and eight to the organ on the other side. 



The elements (triangular bodies) of which the organ 

 is composed appear to be nothing more than greatly 

 enlarged tubercles of the cuticle which have become 

 hollowed out and mounted on short pedicles and arranged 

 in a circular manner around a common centre (tig. '34). 

 The cavity of each of the elements is filled with 

 protoplasm containing a small amount of pigment, but 

 it has not been possible to detect any nuclei. 



Each post-antennal organ is supplied by a small 

 nerve {p.o.n. in fig. 34). 



It is clear that this structure is a sensory organ from 

 the fact of its having a special nerve supply, and the 

 extreme thinness of its cuticular investment shows that it 

 is adapted to receive impressions of external stimuli. 

 What function it is likely to perform is wholly a matter 

 of conjecture; possibly it is an olfactory organ, as is 

 suggested by Willeni. 



The apical sense organ is situated somewhat towards 

 the inner side of the apex of each antenna (Plate I., fig. 7). 

 It is a hollow tri-lobed structure (fig. 8), and its lobes are 

 in free communication with one another at their bases. 

 It is innervated by a branch from the antennal nerve 

 (Plate II., fig. 22), which enters the organ through a small 

 oval foramen situated at its base (fig. 8). 



The function of the organ is uncertain ; Fernald 

 remarks that " the three lobes are so placed relatively to 

 each other that they might easily give the animal some 



