Orf/ans of Sense aiirf Respiration in Ricinulei 131 



hair stands in a small depression, and the surface of the skin round the latter shows a 

 peculiar sculpture with irregular cones, processes flattened down against the surface, and some 

 very small styliform hairs. The small area in which this tactile hair is placed is of markedly 

 different appearance from the surrounding skin, which in Gryptostemma crassipalpe is closely 

 covered with exceedingly small, pointed, almost dentiform granules. On our figure will be 

 noticed, besides, two of the spatulate haiis (A), which occur in small number scattered over 

 the body and limbs. Other organs of sense than the tactile hairs just described we have 

 been unable to discover. 



8. Organs of Reapiratiorh. 



Only one pair of spiracles is found in these Arachnida, and this solitary pair is placed 

 on the cephalothorax. As it would be natural to expect such spiracles as they might possess 

 to be placed on the abdomen we may expressly state that we have examined the abdomen 

 with great care, especially in order to ascertain whether any spiracles existed there, but we 

 have neither found any such in the skin, nor been able to discover any trachea inside the 

 abdomen which could be traced to an origin on the abdomen. 



It was precisely in the last-mentioned manner that we succeeded in finding the spiracles 

 on the cephalothorax, which are otherwise not easily discovered. We noticed the tracheae at 

 an early stage of our investigations, some of them protruding from the bases of a detached 

 antenna and a leg which had been torn off; we followed up this observation by taking out 

 and examining the whole contents of the middle portion and of one side of the cephalo- 

 thorax, whereby several bundles of tracheae and one of the two main trunks were found. 

 This gave us the clue to the whereabouts of the spiracle, whereupon we cut out that portion 

 of the integument on the other side of the cephalothorax, where we concluded the spiracle 

 to be situated, and examined it in connexion with the contents of the same side of the 

 cephalothorax which we had left undisturbed at first. In this way we found the spiracle 

 together with the trunk-trachea belonging to it and the minor tubes originating from it. 



The spiracles are situated near the posterior extremity of the cephalothorax, on the 

 small triangular piece of .strongly-chitiuized integument which is seen inside the lateral border 

 of the cephalothorax above the distal portion of the third pair of coxa;, consequently a trifle 

 outside and in advance of the fore end of the soft lateral skin of the abdominal peduncle. 

 They are therefore not visible on the intact animal. Through lack of adult specimens for 

 dissection we are unable to give a more detailed description of the structure of the spiracles, 

 but must confine ourselves to the statement that the spiracles are rather small, and in shape 

 like a half-moon of which the concavity turns half to the outside, half upwards. The walls, 

 particularly near the opening, ai-e furnished with short, extremely thick, slightly-branching 

 hairs (PI. VII., fig. 1 y), which almost have the character of processes, and at least in part 

 are fi-ee of each other. The short trunk-trachea (PI. VII., fig. 1 x) which originates from 

 the spiracle is of a rather peculiar shape. The transverse section of the basal portion is 

 semilunar, that of the apiical portion is almost circular, and the transition from the one to 

 the other is rather sudden. Taken all together the trachea has the form of a bag, less than 

 twice as long as it is broad, and of which the outer and upper side is deeply depressed, 

 over a little more than its basal half, so as to fit it to the semilunar spiracle. The trunk 

 extends forwards in the cephalothorax, whilst numerous — doubtless several hundred — minor 



17—2 



