Stridulating- Organ in Trechona zebrata. 177 



XXV. — On the Presence of Wood-Mason' s Stridulating- Organ 

 in Trechona zebrata {Walck.). Bj K. I. POCOCK. 



Mr. Thomas Workman of Belfast has recently kindly drawn 

 my attention to the paper entitled " Remarks on the Falces 

 and Maxillae of Spiders," published in the Annals & Mag. 

 Nat. Hist. (3) xix. pp. 258-259, pi. x. %. 3 (1867), in 

 which Mr. John Blackwall describes and figures part of the 

 stridulating-organ of one of the Theraphosidge, wliich he 

 called Mygale zebra. On p. 259, after discussing the inap- 

 propriateness of the term teeth as applied to the abbreviated 

 spines which stud the base of the maxilla and the apex of 

 the labium in the spiders of the family '' Mygalidee," he 

 observes : " but to a remarkable group of spines, situated on 

 the superior surface of the maxillge of Mygale zebra, and 

 clearly indicating, by its position and structure, that the 

 principal function it performs must be that of mastication, the 

 appellation of teeth appears to be more appropriate. Tlie 

 spines composing this group, which are of a dark-brown 

 colour, and have their pointed extremity directed towards the 

 inner margin of the maxillse, are fewer in number, enlarged 

 at the extremity, and much longer and more distinct near the 

 posterior end of each group than the closely compacted ones 

 that form its anterior part. Tiiese spines, by their figure and 

 arrangement, present a highly interesting subject for inspec- 

 tion under the microscope." This description and the figure 

 that accompanies it leave no room for doubt that the author 

 had before him the cluster of modified hairs constituting the 

 notes or keys of the stridulating-organ that was subsequently 

 described by Wood-Mason. That he failed to discover the 

 true significance of the organ is perhaps not surprising, seeing 

 that he had never been previously informed, as had Wood- 

 Mason, that these spiders are able to emit sounds. 



The chief interest, however, of the discovery lies in the 

 fact that Mygale zebra, or rather Trechona zebrata^ as it 

 should be called, is a South-American species; and no other 

 member of the family from this country, which is perhaps, so 

 far as the Theraphosidse are concerned, the richest in the 

 world, is known to possess this stridulating-organ. In fact, 

 in connection with this subject, I remarked, on p. 168 of tiie 

 ' Annals ' for February last, " no organ resemblmg either of 

 those [the two types of stridulators occurring in the oriental 

 genera"^], mentioned above is found in any genus that 1 have 



* See also ' Natural Science,' vi. pp. 44-50. 

 Ann. dfc Mag. N. Hist. Ser. 6. Vol. xvii. 12 



