The External Anatomy of Spiders 



In females the tarsus of the palpus resembles the tarsus of 

 a leg except that it consists of a single segment and bears only 

 a single claw or none. But in the males the tarsus of the palpus 

 is more or less enlarged and is very complicated in structure. 

 As the details of this structure vary greatly in different groups 

 of spiders much use is made of them in classification; for this 

 reason a special discussion of this part is given later. The char- 

 acteristic features of the palpi of males are not fully developed 

 until the spider reaches maturity; in young males the palpus 

 appears merely as a simple club-like organ. 



The Stridulating Organs of the Mouth-parts. — In 

 the sheet-web weavers (Linyphiidos), the external face of the 

 chelicerae is furnished with a file-like series of ridges (Fig. 92) 

 against which the inner face of the femur of the pedipalps is 

 rubbed to produce a sound. And in several genera of tarantulas 

 also the mouth-parts are furnished with stridulating organs. 



THE PALPI OF MALE SPIDERS 



INTRODUCTION 



The remarkable modification of the palpi of the males of spiders into organs 

 for the transference of the seminal fluid to the female at the time of pairing of 

 the sexes attracted the attention of naturalists at a very early date; and the great 

 variety of forms presented by these organs has led systematists to make much use 

 of them in taxonomic work. In practically all of the more important works on the 

 classification of spiders there are figures and descriptions of the palpi of males. 



Notwithstanding the general recognition of the value of these organs for 

 taxonomic purposes our knowledge of their structure is very inadequate. Several 

 important contributions to this subject have been published and are well-known, 

 notably those of Westring ('61), Menge ('66), Bertkau ('75 and '78), Wagner 

 ('87), Van Hasselt ('89), and Chamberlin ('04 and '08). Still we find, even in the 

 more recent publications, figures of palpi given with almost no effort to identify 

 their parts; and even when some of the parts are named we find different terms 

 applied to homologous parts in the descriptions of different genera. 



The necessity of selecting, from the many terms that have been proposed 

 for parts of the palpi, a set to be used in this volume and the need of terms for 

 parts that had not been described led me to make a special study of the subject. 

 The results of this study were published recently (Comstock *io); but the more 

 important of them are repeated here so that they may be available for use in 

 this book. 



THE MORE GENERALIZED TYPES OF PALPI 



In all spiders the external opening of the reproductive organs of the male is 

 on the lower side of the abdomen near its base, in the epigastric furrow. Some 

 time before pairing the seminal fluid is emitted from this opening and is stored 

 in a tubular cavity in an appendage of the last segment of the palpus, where it 

 is retained until the pairing of the sexes, and from which it then passes to the 

 spermathecae of the female. 



The transference of the seminal fluid from the opening of the reproductive 

 organs to the receptaculum seminis of the palpus has been observed by several 



I06 



