336 MR. H. M. BEENAED ON THE 



increase in development (PL XXX. fig. 15). These muscles are very powerful in the 

 anterior abdominal segments, and here belong clearly to a system of muscles which 

 raises the whole abdomen at right angles to the ground ; this, according to Walter (75), 

 being an attitude of defence commonly assumed. It is worth noting that Galeodes can 

 bend the body not only at the waist but also between the 4th and 5th segments. The 

 Galeodidee have thus retained more of the original play of the segments upon each 

 other than any other Arachnid, no other being able to bend the cephalothoracic region. 

 The raising of the abdomen seems to be common to the larger Arachnida, and in Scorpio 

 it has been retained and specialized in connection with the " sting." 



The ventral longitudinal muscles are more specialized than are the dorsal, and anteriorly 

 are not always easy to recognize as such. Commencing in the soft skin at the side between 

 the cephalic lobes and the coxte of the pedipalps and first legs, a band runs backward 

 on each side to be attached to the transverse fold behind the stigmata (PI. XXX. fig. 9). 

 Prom here bands run backward to the next transverse fold and on to the diaphragm. 

 The bands here, both in front of and immediately behind the diaphragm, are very broad 

 and powerful, and apparently counteract the elevators of the abdomen. In the 1st 

 abdominal segment they seem to be continued up the sides of the body (fig. 11) *. 

 In the 2nd segment they take up a more ventral position, almost meeting in the middle 

 line in the 4th segment, from which point they again widen out until in the anal segment 

 they appear to end in the dilators of the anal aperture {G. arabs). 



Longitudinal muscles occur in other Arachnids more or less modified. They are perhaps most highly 

 developed in the abdomen of Scorpio^ owing to the specialization oi' the posterior segments into a tail 

 armed with a stinging-apparatus. This abdomen and tail, as is well known, can (like the abdomen of 

 Galeodes) be raised in the median plane. In Spiders the dorsal muscle-bands are probably atrophied ; 

 the ventral longitudinal muscles, however, stretch I'ight across the posterior portion of the abdomen, 

 at least in young specimens, while anteriorly they taper into bands on each side of the genital 

 aperture (74). Dorsal and ventral longitudinal muscles are also demonstrable in the Pseudoscorpious 

 and Acari. 



All these abdominal longitudinal muscle-bands consist of transversely-striped fibres, although, like the 

 circular fibres, they must be capable of enormous stretching, i. e. wlieu the abdomen is distended. They 

 serve, no doubt, to re-telescope the segments (c/. contracted and distended abdomens, PI. XXIX. 

 figs. 8&9). 



Dorso-ventral Muscles of the Cephalothorax. — These, which are morphologically almost 

 more interesting than the dermal muscles, are found well developed in Galeodes. 



In the cephalothorax there is a system of five pairs of dorso-ventral muscles belonging 

 to segments 4, 5, and 6. These slope and cross each other, running even from one 

 segment into the next. 



The general arrangement of tliese muscles can be gathered from PI. XXX. fig. 9, which 

 was reconstructed from a series of sections and is therefore diagrammatic. Hardly any 

 attempt is made to indicate their relative strengths. It is highly probable that some of 



* Birvda (23) states that normally they are attached to the area in front of the chitinous ridges on the genital 

 opercula (PI. XXIX. fig. 7). This quite confirms my assumption that these ridges are primitive iuterarticular 

 membranes, as shown in fig. 11. 



