Note on the Cœlomic Cavity of the Spider. 



by 

 K. Kishinouye, Riè^kushi. 



Zoologist to the Department of Agriculture and Commerce. 



With Plate X. 



The species investigated belong to the genera, Lycom and 

 Agaleiui. 



My olyject in undertaking tliis investigation was to ascertain 

 whetlier the stercoral pocket is mesoderinic in origin as I described in 

 my former paper* or ectodermic and a part of the proctoda^um, as is 

 generally believed. 



When the embryo has reached the stage in which there are nine 

 segments in the ventral plate, i.e., seven segments between the cephalic 

 and caudal lobes, the mesoderm is divided into as many segments, 

 while a ]3air of the cœlomic cavities appears almost simultaneously in 

 each of the first five segments, exclusive of the cephalic lobe (Fig. 1).** 

 As at this stage the segment of the cheliceroe is not yet formed, 

 the cœlomic cavities now formed belong to the segments of the pedi- 

 pal]ii and the four ambiTlatory appendages. The rudiments of appen- 



* On the Development of Araneina. This Journal, vol. IV. 

 ** As the segmentation of the ventral plate seems to take place simultaneously with the 

 division of the mesoderm into somites, I will hereafter for the sake of brevity, simply describe 

 the formation of a segment and will not mention every time the formation of the correspond- 

 ngc mesodermic somite. 



