Fig. 117. THREE TYPES OF EMBOLUS 



The External Anatomy of Spiders 



In the free type, the embolus varies greatly in form; but the different forms can 

 be grouped under three heads; coniform, iamelliform, and spiral. 



A coniform embolus. — In this type, there may be a broadly expanded base; 

 but the projecting part of the embolus is a straight or slightly curved cone. The 

 embolus of Aranca jrondosa (Fig. 117, 1.) is an example of this type. 



A Iamelliform embolus. — In this type the embolus is flattened, and may bear 

 a greater or less number of apophyses; an example of this type is found in Leptby- 

 pbantes minuta (Fig. 117, 2.). 



A spiral embolus. — - In the spiral type, as seen in Agelend, for example, the em- 

 bolus is long, slender and coiled; and, in a well-expanded specimen, it is seen to 



be composed of three 

 distinct parts; first, the 

 wall of the convex side 

 is densely chitinized, 

 forming a gutter-like 

 sclerite, which may be 

 termed the trunk of the 

 embolus (truncus) (Fig. 

 117, 3, t. f.); second, 

 the greater part of the 

 wall of the embolus is 

 membranous, and forms 

 a loose flap along the 

 concave side of the or- 

 gan, which contains the 

 ejaculatory duct; this 

 flap (Fig. 117, 3, p. p.) 

 may be designated the 

 pars pendula of the em- 

 bolus; third, at the dis- 

 tal end of the pars pendula, there is a triangular, chitinized area, through whicli 

 the ejaculatory duct opens (Fig. 117, 3, a. s.), this may be termed the apical 

 sclerite of the embolus. 



The pars pendula and the apical sclerite may be completely withdrawn into 

 the trunk of the embolus, so that only the latter is visible; the embolus then appears 

 to be merely a strongly chitinized style; it is in this condition that it is usually 

 seen and described. 



CONCLUSION 



In the preparation of this account many palpi other than those figured here 

 have been studied; and it is believed that the series examined has been sufficiently 

 large to warrant the conclusions given regarding the fundamental parts of the 

 genital bulb. There remains to be determined the manner in which the different 

 types of palpi have been specialized in other families of the order, and the details 

 of the modifications characteristic of genera. This, however, is too great an under- 

 taking to be attempted at this time; and must be left for those who monograph 

 the different families. 



I wish, however, to urge the importance of describing palpi from expanded 

 specimens. A large proportion of the figures of palpi that have been published 

 being of unexpanded examples, show comparatively little of the structure of this 

 organ. The labour involved in expanding the bulb of a palpus is very little; 

 a preparation can be made in five minutes; and in no other way can so much be done 

 to make possible a description that will describe. 



The following tabular statement shows the relations of the fundamental 

 parts of the tarsus in the more specialized types of palpi; not all of these parts are 

 invariably present, and frequently subordinate apophyses are developed. 



Body of the Tarsus 



C/mbium, containing the alveolus 

 Tutaculum (in the Thomisida?) 

 Paracymbium 



120 



