300 PROCEEDINGS OF THE ACADEMY OF [May, 



Aviculariidse possess only two pairs/ and the Atypidse (the genus 

 Brachybothrium excepted) possess three pairs. Almost all the Aranese 

 verse have three pairs of spinnerets. 2 These discrepancies in number 

 make it somewhat difficult to homologize the pairs of different groups, 

 a difficulty briefly mentioned by Stevenson (1908). 



The three pairs of spinnerets found in most of the Aranea? verse 

 are named in antero-posterior order: the anterior (inferior), the 

 median, and the posterior (superior). Between the spinnerets of the 

 anterior pair may be placed either a cribellum or a colulus, both of 

 which are absent in the Theraphosse. The cribellum was discovered 

 by Blackwall (1839), and has been most thoroughly described by 

 Bertkau (1882) as a small transverse plate, sometimes halved by a 

 median carina, this plate provided with the very numerous minute 

 pores which are the openings of multicellular spinning glands, and the 

 spinning plate enclosed in a chitinous frame. In species possessing 

 it the fourth pair of metatarsi are each provided with a row of recurved 

 hairs, called the calamistrum and also dicovered by Blackwall; the 

 latter is used as a comb to draw out the silk issuing from the cribellum — 

 an operation that can be clearly seen in the larger species of Filistata, 

 though it is performed with great rapidity. In mature males the 

 cribellum is more or less rudimentary, for which Bertkau offers the 

 valid explanation that adult males do not spin snares. Blackwall 

 and Bertkau correctly interpreted the cribellum as a modified and 

 fused pair of spinnerets, while Thorell (1870), who called it the "infra- 

 mamillary organ," argued against such a comparison, though without 

 cogent reasons. 



The colulus or hypopygium (Menge, 1843) is a conical projection or 

 small tubercle occupying approximately the place of the cribellum 

 in some of the families of the Aranese verse which do not possess the 

 cribellum. It has no spinning glands and there is no calamistrum 

 associated with it. Menge compared it with a rudimentary cribellum, 

 but Bertkau argued that the colulus is a simple integumentary fold 

 representing the region between tracheal stigma and cribellum. 



To decide with which of the three pairs of spinnerets of most Aranese 

 the two pairs of most Aviculariidse correspond, I have examined some 



1 The exceptions are the genera Hexathele and Scotinctcus with a third (most 

 anterior) pair of very small spinnerets; and Anisa pis and Diplothele with only 

 one pair. 



2 According to Simon, I.e., less than three pairs are exhibited by the following: 

 the Hadrotarsidae, Palpimanidse (except Huttonia) , the Zodariid genera Lutica, 

 Hermipus, Mediums, and the Archseid Mecysmauchenius — these named genera 

 having only one pair. 



