COMPAEATIVE MORPHOLOGY OF THE GALEODID.'E. 367 



they run where there once was an inter-diverticular infolding of the membrane. I was at first inclined 

 to believe that they had borrowed these fibres from the dorso-ventral muscles, but now think that they are 

 developed out of the remains of the membrane. I am led to this belief by noticing that, in Thelyphonus, 

 while the dorso-ventral muscles run outside the long fourth pair of diverticula (PI. XXXIV. fig. 2), 

 the " veno-pericardial " muscles run iuside between these diverticula and the hind-gut, but where 

 segmental diverticula once existed but have now disappeared. The veno-pericardial muscles persist as 

 their last vestiges. 



In Tfiefi/jjhoims we have two pairs of these muscles in the cephalothorax, attached ventrally to the 

 eudosteruite, and in the abdomen seven pairs *, raising up the membrane ventrally in each segment to 

 form a pair of blood-spaces. Further, in Scorpio, we also have seven pairs in the abdomen. The 

 morphological importance of these series of ventral blood-spaces connected by fibrous and muscular 

 strands with the heart, and alwnys accompanying the ostia, will be discussed in the section on rcsjiiration. 



In both Scorpio and Tiiehjphonus the circulation is further specialized by the presence of short 

 connections between the heart and the membrane surrounding the diverticula. They are short muscular 

 (valvular?) funnels liy which the blood can be pumped directly under the membrane, where it can 

 circulate through a system of blood-spaces with thin membranous walls among the diverticula (PL XXXIV. 

 fig. y). There are nine pairs of these iu TheltjphoHUS. Lankester describes seven pairs ("arteries") in 

 Androctonus -. I have only succeeded in finding five pairs in a small Euscorpio ; there may, however, be 

 seven, as in Androctonua, although five is the number of alimentary diverticula which they have to supply. 



In the Pseudoscorpions the heart seems to vary, according to the observations recorded, as to the number 

 of ostia. According to Croueberg (27), there are three jiairs ; according to Winkler, one pair j and according 

 to Daday (29), there are four pairs and a certain number (4) rouud a rosette-like terminal portion. 



In a series of cross- sections of Obisiiim, in which the heart was well distended, it was found to commence 

 (from behind forward) iu about the same trausverse plane with the hind-gut (PL XXXIV. fig. 3). The 

 posterior aperture was very wide (36yti), and, being dorso-ventrally flattened, would, seen from above, 

 have a fan shape, which may be Daday's rosette. The posterior lips were irregular, which maybe due to 

 valvular infoldings. From the posterioi opening, the heart, suspended in the typical way, rapidly narrowed 

 to J- (IS/"') of its posterior width, and then widened again (20 yu.) to form one chamber. This chamber 

 has the typical appearance, and is fastened by the wing-like groups of fibres converging downward towards 

 the dorso-ventral muscle, apparently to lose themselves among the diverticula. From this point the heart 

 narrows to form an aorta. The whole structure is thus very minute, with, as Winkler stated, only one 

 pair of ostia. As in Guleudes, its insignificance peiliaps has some connection with respiration by means of 

 tracheiie. 



In Fhrynus we have six pairs of ostia, which correspond with six pairs of abdominal ostia in Galeodes. 

 We find the same mechanism as in Thcli/phomis and Scorpio to protect the circulatory system from undue 

 pressure when the abdomen is distended, viz., the veno-pericardial muscle- strands. 



The heart of the Spiders is fairly well known ; it is entirely confined to the abdomen. From it, as 

 iu the last three families mentioned, an anterior aorta runs into the cephalothorax. There is a highly- 

 developed pericardium, no doubt specialized from a membrane enveloping the alimentary system, 

 surrounding and protecting the heart from undue pressure when the alimentary tubules are distended 

 by a full meal. In some Spiders, e. g. Epcira, these tubules may eveu grow up on each side of the 

 pericardium so as to force it, with the heart, away from the dorsal wall f- Foi" the protection of the 

 heart, the pericardium is fastened back by a system of strands, which appear to lose themselves among 

 the alimentary tubules. There are three [Epeira) or four {Mijgale %) pairs of ostia, 



* This implies that there were once at least twelve pairs of primary alimentary diverticula (see the diagram 

 PL XXXIII. fig. 12). 



t Cf. Schimkevitch (62), pi. ii. fig. 9. t Wasmuiin (74 rr). 



