816 Pomona Coi.lege Journ-U. of Entomology 



with tlio nerve fibre. This result was criticised and the nerve terniinatioQ was 

 found to be exaggerated in thase eases. In some Crustacea it wa.s found that 

 the base of the hair was shut off from the shaft so that no nerve strand could 

 penetrate very far into it. In insects most of the hairs seem to be 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 nuieh, but a study of the hairs 

 seems 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 simjile 

 type and without 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 intere-sting to note in this 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 seti? 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 diplopod.s 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 

 ScoJopendra where the hairs were minute projections only. These simple 

 types .show something of how sets 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 littl# projections with mounds 

 and without them. 



The generalized Peripatus is interesting to examine in this connection. 

 Here we find the predominating sensory projections are little elevations; 

 some of these 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 sensory structures of 

 spiders with some experiments on the functions of the setiv. 



Important References 

 1912 Berlese, A. Thrcmibidiidiv " Bcdia." Vol. VIII. 



1896 Bethe, Das Nervcn.system von Careinus menas, Anh. f. Mie. An<it. 



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



ann. de I'Univ. de Grenoble. 

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

 poden. Anal. Am. 1895. 



