COMPARATIVE MOBPHOLOGT OF THE GALEODID.E. 313 



body. They were, perhaps, at first obliterated at the anterior end of the body, or rather converted into 

 the labium by the grouping of the two first pairs of limbs round the mouth (see p. 311), and then 

 secondarily, in the genital segment, by the change of a pair of limbs into genital appendages (see p. 328, 

 and PI. XXIX. fig. 14). 



The Numhev couJ Character of the Abdominal Segments. — The abdomeu in the Galeodidse 

 consists of ten segments, which, as above stated, are distinct. They are fairly iiiiifonn, 

 i. e. they ta^oer away in a typical manner, showing no specialization into a tail of any 

 kind. The last segment is little more than an anal jjapilhx except in Ilhax. The cuticle 

 is adapted for the great extensions to which the abdomen is liable. After a full meal 

 the abdominal region may be nearly twice as thick and twice as long as at ordinary 

 times. While the ventral and dorsal surfaces are protected by more solid chitinous plates 

 (tergites and " sternites " *), the intersegmental and lateral integuments are very thin 

 and flexible. Fig. 6, PI. XXXIV., shows the remarkable folding of the integument 

 between two segments of a contracted abdomen ; this is even more pronounced in the 

 more anterior segments. The fine structure of this flexible integument will be described 

 elsewhere. 



Great variations are found in the hairiness of the abdomen. Swollen abdomens often 

 look smooth, owing to the drawing apart of the hairs, which in the contracted state 

 would be crowded together. For this reason, contracted specimens are often very 

 hairy. This, however, does not explain the whole facts. In some, the lateral membranes 

 are smooth, in others hairy. The " sternites " are smooth, in others again hairy. The 

 hairiness of the lateral membrane is often felt-like ; that of the " sternites " repeats that 

 of the cox0e of the legs. 



The number of segments in the abdomen of Arachnids varies considerably. The greatest number, 

 twelve, occurs in Thelyphonus, Phrynus, and Scorpio, and, according to Mr. Pocock, in Schizonotus. 



The abdominal segmentation of the Pseudoscorpiouidte is very difficult to unravel. The anal papilla 

 may perhaps represent a segment, but there are reasons for believing that it does not. But whether the 

 first free tergite, in those cases in which there are undoubtedly eleven tergites, belongs to the abdomen 

 or to the cephalothoras I have been unable to determine. In view of the free cephalothoracic segments 

 of Galeodes and Schi-onoiiis, and the absence of a marked waist, either interpretation is possible. I 

 suggest that the point may be settled by a careful examination of the dorso-ventral muscles. I do not 

 agree with Hansen (33) in claiming the ti'iangular piece sometimes seen behind the coxae of the last 

 pair of legs as belonging to the first abdominal segment, but think that it belongs to the last cephalo- 

 thoracic segment, and, as in Thelyphonus and Galeodes, has been left bare by the inner anterior slope 

 of the coxse. But the Chernetidse show great and puzzling variations. In some there is a clear 

 triangular piece in front of the genital plate ; in others the last pair of coxae seem to reach back so as 

 to cover, ventrally, the anterior segments of the abdomen (lO; compare figs. 1 & 2). 



In the Spiders there are, as a rule, tea se^^ments, while in the Phalangidae and in some Acariuae the 

 number is still further reduced. 



This difference in the number of abdominal segments is not a matter of any great morphological 

 importance. The specialization of the Arachnids has clearly taken place at the anterior end of the 

 body, in the grouping of the first two pairs of limbs round the mouth and in the development of the 

 limbs of the four following segments as walking-legs. This cephalothoracic region, specialized for loco- 



* As above stated, I do not consider them to be morphologically sternites, but rather limb-areas, i. e. areas where 

 limbs have vanished by flattening down. 



SECOND SERIES. — ZOOLOGY. VOL. VI. 42 



