SENSORY CANALS OF LJEM ARGUS. 69 



wards nearly at right angles to the long axis of the head, and passes downwards behind 

 the orbit. Having reached the ventral aspect, it communicates with the hyomandibular 

 canal (HM., fig. l), and then bends forwards and inwards to meet and communicate with 

 the supra-orbital canal (S.O. 4 , fig. 1), as it turns sharply inwards towards the middle line. 



On the way it forms a characteristic forward projecting loop (I.O. 3 , fig. 1). On reach- 

 ing the middle line it blends, for a short distance, with the corresponding canal of the 

 opposite side (I.O. 4 , fig. 1). Leaving its fellow it runs outwards and forwards to sink 

 well into the substance of the snout, and terminate blindly about 6 mm. from its anterior 

 margin, and 1^ cm. from the middle line (I.O. 5 , fig. 1). This canal corresponds to the 

 orbital (orb.), suborbital (so.), orbito-nasal (o.n.), nasal (n.), median (half of) (m.), and 

 prenasal (pn.), canals of Garman (figs. A and B). 



In diameter the infra-orbital resembles the supra -orbital. Narrow at first, it 

 gradually widens until it reaches the side of the head, where it contracts slightly, to 

 again expand as it reaches the under surface. With the exception of the median and 

 terminal portions, the ventral part of the canal has a diameter of from 3 to 4 mm. 



The median portion is from 5 to 6 mm. wide, while the terminal portion varies from 

 2 to 3 mm. The canal, at first in contact with the skin, soon sinks to a depth of 5 mm., 

 but on reaching the level of the spiracle it again approaches the surface and remains all 

 but in contact with the skin until it joins the hyomandibular. Between this canal and 

 the supra-orbital, it lies at a depth of nearly 5 mm. ; but as it bends inwards it becomes 

 more superficial, lying at a depth of 3 mm. until it reaches the under surface of the 

 rostrum, where it sinks to a depth of 5 or 6 mm., and finally, at its termination, to a 

 depth of 1 cm. 



Eighty-seven twigs from the buccal nerve were found penetrating this canal to reach 

 and end in a corresponding number of sense organs. Of these nerves there were 24 in 

 the first part of the canal (orbital and suborbital), 11 in the second (orbito-nasal), 23 in 

 the third (nasal), 3 in the common median part, and 26 in the terminal (prenasal) part. 

 The nerve pores varied considerably in their arrangement ; near each other at first, they 

 became less numerous in the descending part of the canal, after which they were fairly 

 regular with the exception of the anterior (prenasal) part, in which they were especially 

 abundant. The distribution of the fibres of the buccal to the nerve hillocks is indi- 

 cated on the right side of figure 1. 



This canal opens through the skin by tubules similar to those of the supra-orbital. 

 Altogether 86 tubules were counted, and, as a rule, they proceeded from the canal 

 opposite the pores for the entrance of the nerves. The majority of the tubules varied in 

 length with the distance of the canal from the surface ; the dorsal tubules extended 

 backwards ; the majority of the ventral directly outwards ; but those from the terminal 

 portion of the canal projected outwards and forwards. The irregular ventral part of the 

 infra-orbital canal comes into intimate relation with numerous ampullary canals ; the 

 openings of some of which are with difficulty distinguished from the openings of the 

 tubules. 



