COMPAEATIVE MOEPHOLOGY OF THE GALEODID^. 337 



these are true dorso-veutral muscles much modified and shifted in adaptation to the 

 special movements required. For instance, none of theiu meet ventrally in the middle 

 line as the undoubted dorso-veutral muscles of the abdomen do, and as these ought to do^ 

 owing to the approximation of the coxa) in the middle line. All these muscles are situated 

 more or less laterally ; hence it is also possible that some of them may be adaptations of 

 circular muscles. The point requires to be specially worked out. The general action of 

 these muscles can be gathered from the figure. 



The relations between these dorso-ventral muscles and the alimentary canal will be discussed in the 

 section on the latter sj'stem. We may, however, mention that this inter-relation teaches us that the 

 four pairs of alimentary diverticula in the cephalothorax, which are characteristic of Arachnids, indicate 

 the former presence of at least four pairs of dorso-ventral muscles in the cephalothorax, running in the 

 dividing planes between the last four segments. Whether any, and, if so, which of the five pairs of 

 dorso-ventral muscles in the posterior ccphalothoracic segments of Guleodes answer to the hypothetical 

 four, it is now difEcult, if not impossible, to ascertain. The last, inasmuch as it runs behind the last 

 cephalothoracic diverticulum instead of in front of it, probably belonged to the constriction which formed 

 the diaphragm. 



In Scorpio only one pair is retained, viz. that in the last cephalothoracic segment ; it runs down in 

 front of, but not in contact with, the diaphragm, and is attached to the endosternite. This agaiu 

 probably belonged originally to the intersegmental constriction which formed the diaphragm. 



In Phrynus, Thelyphonus, and the Aranece four pairs of dorso-ventral muscles have been retained more 

 or less modified as the dorsal attachments of the endosternite, and are now largely fibrous ; they suspend 

 the endosternite, on which the alimentary canal rests, and separate the alimentary diverticula in the 

 typical manner. If the endosternite of Guleodes were attached by fibres to the dorsal wall, these would 

 apparently represent the dorso-ventral muscles of the constriction behind the 3rd and 4th segments. I 

 find in my dissecting-notes that there is such a fibrous attachment, but I unfortunately did not record 

 the exact position. 



In the Spiders the powerful muscles from the dorsal wall to tiie sucking-stomach are probably not 

 adaptations of dorso-ventral muscles, but to be derived from the original oesophageal or pharyngeal 

 muscles which are now variously developed, i.e. according to the position of the sucking- apparatus in 

 relation to the nerve-mass (on the position of the sucking-stomach in Spiders, cf. the section on the 

 alimentary canal). 



In the Psudoscorpions there is one pair behind which the 1st alimentary diverticulum expands. It 

 therefore apparently belonged originally to the constriction between the 2nd and 3rd segments. 



The diifcrent ways in which these cephalothoracic dorso-ventral muscles have been retained is quite 

 in keeping with the various methods of longitudinal compression which the cephalothorax has undergone 

 {cf. the various developments of the diverticula in the alimentary canal). 



In the Scorpions, Pscudoscorpions, and Thelyphonidse, muscles descend from the anterior dorsal surface 

 near the median line to the labrum. These are, apparently, the original longitudinal muscles running 

 to the labrum, which now run dorso-ventrally owing to the present depressed position of the labrum. 



Dorso-ventnd 3Iuscles in the Abdomen. — There are six pairs of dorso-ventral muscles 

 in the abdomen of Galeodes belonging originally to the constrictions between the first 

 seven segments (PI. XXX. fig. 9). The majority of them seem now to have two 

 points of attachment, viz. partly to the segmental constrictions — the primitive arrange- 

 ment — and partly to the middle of the segments, which is a specialization found in 

 many otlier Arachnids. Dorsally, these muscles are inserted on each side of the heart 



SECOND SERIES. — ZOOLOGY, VOL. VI. 45 



