The External Anatomy of Spiders 



The Linyphia Type of Palpus. — The very common Linyphia phrygiana 

 will serve as an example of the Linyphiidae. 



As in Pacbygnatha, just described, the body of the tarsus of Linyphia consists 

 of two parts; the cymbium (Fig. 102, cym.), and the paracymbium (Fig. 102, p. c). 

 The alveolus is a circular- cavity near the base of the cymbium. 



When the bulb is expanded, the three divisions of it are distinctly separated; 

 there being a slender neck between the basal division (Fig. 102, b. d.) and the middle 

 division (Fig. 102, m. d.) and also a similar slender neck between the middle di- 

 vision and the apical division (Fig. 102, a. d). 



The wall of the basal division of the bulb consists of two parts; the basal 

 hasmatodocha, and the subtegulum. 



The basal hamatodocha. — The genital bulb is attached to the cymbium, 

 within the alveolus, by means of a sac-like structure, which, ordinarily, is incon- 

 spicuous or completely concealed by other parts of the bulb, but which is very 

 conspicuous in the expanded bulb (Fig. 102, b. /;.). This has been named the 

 hamatodocha from the fact that at the time of pairing it is distended with blood. 

 The wall of the haematodocha appears to consist of elastic connective tissue; 

 hence the name spiral muscle applied to it by Menge is inappropriate. In fact 

 no muscle tissue has been found within the genital bulb. As similar extensible 

 blood sacs are present in more distal parts of the bulb of many spiders, 1 suggest 

 that this one be termed the basal hccmatodocha. 



The subtegulum. — The proximal end of the basal haematodocha is attached to 

 the cymbium, the distal end, to a ring-like sclerite, for which 1 propose the term 

 subtegulum (Fig. 102, s. teg.) . 



The middle division of the bulb. — The middle division of the bulb (Fig. 102, 

 m. d.) is that part which contains the chief portion of the receptaculum sem- 

 inis, the reservoir; its wall is the tegulum, and it bears an appendage, the median 

 apophysis. 



The tegulum. — The term tegulum was applied by Wagner to all of the more 

 densely chitinized parts of the wall of the genital bulb; but as it is desirable that 

 the different sclerites should bear distinctive names, I propose that this term be 

 restricted to the sclerite that forms the wall of the middle division of the bulb. 

 In Linyphia, the tegulum, in this restricted sense is a ring-like sclerite (Fig. 102, 



teg.). 



The median apophysis. — Arising within the distal margin of tegulum there 

 is an appendage, only the tip of which is shown in the view of the bulb figured here 

 (Fig. 102, m. a.); this is the median apophysis. In many spiders this appendage 

 is very conspicuous; and to it have been applied several names. In fact in several 

 instances a writer has applied different names to this part in his descriptions of 

 different genera. Among the names that have been applied to it are clavis, unca, 

 and scopus. The term median apophysis occurs frequently in descriptions, and 

 is the older name for this part. 



The median apophysis is articulated to the middle division of the bulb near 

 the point from which the apical division arises; and in some cases, as in Aranea, 

 it appears to be more closely articulated with a basal segment of the apical di- 

 vision, the radix, than it is with the tegulum. 



The apical division of the bulb. — This division includes that portion of the 

 bulb which lies distad of the middle division; it consists of two subdivisions: the 

 conductor and the embolic subdivision. The embolic subdivision is traversed 

 by the ejaculatory duct and is composed of several distinct parts. In fact the 

 multiplication of parts of the embolic subdivision is the most characteristic feature 

 of the more specialized types of palpi as contrasted with the intermediate type 

 described above. 



The conductor. — The conductor (Fig. 102, con.) is easily recognized by its 

 relation to the embolus, which rests upon it, and by its membranous texture. 

 Its attachment to the middle division of the bulb is by means of an exceedingly 

 delicate membrane. 



In Linyplna the embolus rests upon the conductor throughout its length; 

 but in many genera the palpi of some of which are described later, the function 

 of the conductor is evidently to protect the tip of the embolus in the unexpanded 



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