816 Pomona College Journal of Entomology 



with the nerve tilire. 'I'his result was criticised ami the nerve termination was 

 found to be exagjrerated in these cases. In some Crustacea it was found that 

 the liase of the liair was sliut off from tlie shaft so that no nerve strand could 

 penetrate very far into it. In insects most of the hairs seem to l)e hollow 

 from base to tip or nearly to the tip, with often some granular substance in 

 the cavity. In work done with methylene blue and sections of material 

 stained by this method nerve fibres were traced into the hairs but only a 

 short distance into the shaft, Hilton (1902). As yet the few injections which 

 have been tried with tarantula have not shown much, but a study of the hairs 

 seema to show no barrier to the penetration of the nerve fibre. It seems 

 doubtful, however, whether the very long hairs of tarantula contain nerve 

 fibres in very much of their length. 



In tarantula many hairs which at first sight seem to be of the simple 

 type and witliout pubescence are found under higher powers of the micro- 

 scope to show delicate projections. It is probable that hairs of this sort are 

 of wide occurrence. It is interesting to note in tliis connection that the hair 

 shown in Figure 3, Plate III, in Villane's ('81) early paper on the histology 

 of insects is of this type. 



Among the sets' of other arthropods exclusive of Crustacea, spiders and 

 insects, we find the simple hair of medium size the most usual type. In some 

 of the hairs of diplopods we find thick hairs with a very small central cavity 

 beyond the base. In Pedipalpida there is a simple type in the sort of hair 

 which projects from a mound. Very simple types of hairs were found in 

 Scolopendra where the hairs were minute projections only. These .simple 

 types show something of how seta^ may have developed, as little knobs on 

 the surface which became sensitive by means of a more or less definite nerve 

 termination and later came to grow out longer and form a hollow projection 

 and develop a collar from the little mound at the base. We have all stages 

 shown in the figures: the little mounds, the little projections with mounds 

 and without them. 



The generalized Prripatus is interesting to examine in this connection. 

 Here we find the predominating sensory projections are little elevations; 

 some of the.se become farther specialized by secondary knobs and now and then 

 from these last, little hair-like hollow projections have been formed. 



It is hoped at a later date to make a study of the sen.sory structures of 

 spiders with some experiments on the functions of the seta;. 



Important References 

 1912 Berlese, A. Thrombidiidiv "Nrdia." Vol. VIII. 



1896 Bethe, Das Nervensystem von Carcinus menas, Arch. f. Mie. Anat. 



1897 Duboscq, 0. Sur la termination des nerfs sensitifs des chilopods 



ann. de I'Univ. de Grenoble. 

 1895 Holmgren, E. Zur Kenntniss des Ilautnervsystems der Arthro- 

 poden. Anat. Am. 1895. 



