158 ALEXANDER PETRUNKEVITCH 



remarkably good and that prolonged sojourn in the preserving 

 fluid made the material considerably less brittle than it usually 

 is on account of the voluminous yolk. A cursory examination of 

 the sections has revealed so many interesting deviations from the 

 usually accepted descriptions of the anatomy and embryology 

 of scorpions, that a number of carefully oriented and sectioned 

 series of various stages were made. All sections were purposely 

 made 20/^ thick. Exact orientation for sagittal, frontal, and 

 transverse series was comparatively simple on account of the 

 size, shape, and coloration of the material. A few of the series 

 are absolutely symmetrical. The most satisfactory staining 

 proved to be haematoxylin followed by orange G. 



When the studj^ of the circulatory system revealed the remark- 

 able similarity in this respect between scorpions and spiders, 

 T prepared corresponding series through very young spiders 

 fixed for the purpose in my sublimate mixture. Two species 

 of scorpion ('Centrums insulanus and C. carolinianus) and three 

 species of spiders (Agelena naevia, Lycosa carolinensis, and 

 Pholcus phalangioides), belonging to three different families, 

 form the basis of the present studj^ While it would be very 

 interesting to extend it over other groups of Arachnida, the 

 diversity of the material leaves no doubt that similarity here is 

 not accidental, but is the expression of true homology, and 

 that generalization is therefore warranted and helpful." 



To avoid possible misinterpretation of results, obtained only 

 from the study of sections however perfect, a few scorpions 

 were injected through the heart. These scorpions, Centrums 

 carolinianus of Texas, were obtained alive through the courtesy 

 of Professor Painter, of the University of Texas, who kindly 

 took the trouble to collect and mail to me a dozen specimens. 

 Injection was made in a manner similar to that which I used for 

 Lycosa several years ago, but the technique in the case of the 

 scorpion is somewhat more complicated, owing to the fact that 

 the heart is only imperfectly visible through the chitin. For 

 this reason it becomes necessary to open the chloroformed speci- 

 men in a saline solution to expose the heart. The tergites of 

 the second to sixth abdominal segments are carefully removed, 



^ 



