I06 C. W. STEVENSON. 



review ; and descriptions of the external anatomy of the spin- 

 nerets given by Simon (1892). 



Therefore the spinning glands of Theraphosids are practically 

 unknown and the present contribution is to present an account 

 of a member of that group, and was done under the direction of 

 Prof. Thos. H. Montgomery, Jr. 



Simon (1892) divides the spiders into Aranece Theraphosa: and 

 AranecB Verce, the former including all spiders with chelicera 

 directed forward, and comprising the families Liphistiidae, Avic- 

 ulariidje and Atypidse. The Liphistiidae are unique among all 

 spiders in having four pairs of spinnerets ; the Aviculariidae have 

 only two pairs (except Hexathele which has three), while the 

 Atypidse as also most of the families of Aranece VercB, possess 

 three pairs. 



There has been a discussion as to the homologies of the two 

 pairs of spinnerets of the Aviculariidae with the three and four 

 pairs of the Atypidae and Liphistiidae. Jaworowski (1895) has 

 shown that in Lycosids the embryonic extremities of the fourth 

 and fifth segments of the abdomen give rise to the spinnerets in 

 the following manner : each extremity of the fourth segment con- 

 sists of two parts, endopodite and exopodite, of which the exopo- 

 dites give rise to the anterior pair of spinnerets, while the endo- 

 podite of one side fuses with its fellow of the opposite side to form 

 the colulus or its homologue the cribellum. As for the extremities 

 of the fifth segment, the endopodites give rise to the median pair of 

 spinnerets and the exopodites give rise to the posterior pair. 



Now, it is possible, as Jaworowski believed, that of the four 

 pairs of spinnerets of the Liphistids, the most anterior pair is 

 homologous with the colulus and cribellum of the Aranccc 

 VercB. But just what are the homologies of the three pairs of 

 spinnerets of the latter to the two pairs of the Aviculariidae can- 

 not yet be decided, as the embryology of no Theraphosid has 

 been worked out, although Simon considers the two pairs of the 

 Aviculariidae to correspond to the anterior and median spinnerets 

 of other spiders, while Jaworowski would hold them as homolo- 

 gous with the anterior and posterior spinnerets of other spiders. 

 Accordingly in calling the spinnerets of Evagrus "anterior" and 

 "posterior" respectively, following the general usage, I do not 

 mean to prejudice the question of their homologies. 



