164 ALEXANDER PETRUNKEVITCH 



(not eight as usually erroneously stated). The presence of the 

 ostia gives the heart the appearance of an eight-chambered organ. 

 In reality there are neither valves nor any constriction or im- 

 pediment in the spaces between the successive ostia. There is, 

 therefore, nothing that would have the morphological value of 

 chambers. In transverse sections the ostia occupy a position 

 approximately half-way between the dorsal pole and the equator 

 of the heart. The first pair hes exactly at the posterior edge of 

 the first abdominal tergite. The position of all seven pairs may 

 be best understood from text figure A. It is the same in all 

 specimens and does not change with maturity. The structure 

 of an ostium with its valve is represented in figure 3 on a large 

 scale. This is a frontal section, and the media or muscularis 

 is therefore sectioned at right angles to its muscle fibers. Each 

 fiber has the appearance of a rectangle. The adventitia of con- 

 nective tissue is well defined and shows long, darkly stained 

 nuclei. Multinuclear fibers of connective tissue run from the 

 edges of the ostium laterally, converging and forming a ligament, 

 the so-called pteripyle. 



The position of the ligaments by which the heart is suspended 

 is well lal0^vn in spiders, owing to several researches, especially 

 those of Causard. There is scarcely any difference in this respect 

 between spiders and scorpions. Text figure B, drawn from a 

 complete series of transverse sections through a late embryo, 

 represents the heart of the scorpion with all its ligaments of a 

 single group projected into the same plane. All told, there are 

 eight metamerically arranged groups of ligaments, each group, 

 except the first, composed of four pairs. The shortest of these 

 are the epicardiac ligaments which pass on each side of the dorsal 

 sinus and are attached to the basal membrane of the hypodermis, 

 thus clearly demonstrating their connective nature, since all 

 muscular fibres, as for example those of the dorsoventral muscles 

 represented in the figure, pass between the hypodermal cells 

 and are inserted in the base of the cuticle. The second pair are 

 the pteripyles. Their distal end merges with the somatic con- 

 nective-tissue layer which separates the dorsal longitudinal 

 muscles of the abdomen from the hypodermis. The third pair. 



