NOTE OX THE CŒLOMIC CAVITY OF THE SPIDER. £93 



Their proximal and outer portions remain distinct at the base of each 

 leg (Fig. 9). The cœlomic cavity of the first ambulatory appendao-e 

 communicates with the exterior by means of a duct which is produced 

 by an ectodermic invagination. The first abdominal segment disap- 

 pears entirely. 



The mesodermic moieties of the second to fifth abdominal se»-- 



o 



ments, or the segQients bearing the provisional appendages, meet 

 one another at the dorsal median line and form there the wall of the 

 heart. The wall of the cd'lomic cavity of the second abdominal seg- 

 ment meets that of the cephalic lobe (Figs. 9, 10). The forma- 

 tion of tlie dorsal circulatory system, in which some thoracic somites 

 do not take part, resembles greatly that of Limulus.* As a lateral slit 

 or ostium is made where two consecutive somites meet, the number 

 of the slits in the adult heart shows approximately the number of the 

 segments which took part in the formation of the heart. 



The sixth to eighth abdominal somites are entirely degenerated, 

 their mesoderm cells are disintegrated and fill the caudal lobe at the 

 sides of its unpaire 1 cœlomic cavity (Figs. 9, 10). The latter becomes 

 wide, and over its posterior end, the ectoderm is slightly invaginated 

 (Fig. 9). The invagination is the rudiment of the proctodeum, so 

 that the unpaired cavit}^ of the caudal lobe is produced independently 

 of the proctodeum. 



In the next stage in which the embryo assumes the ventral 

 flexure and the constriction between the céphalothorax and the abdo- 

 men appears, the cœlomic cavities undergo great changes. In the 

 céphalothorax, they all disappear, except the small portions at the 

 outer bases of the first to third ambulatory legs. These remnants 

 fuse together and form the coxal gland (Fig. 12). The lumen or the 



* Kishiuouye — On the Development of Limulus longispina. This Journal, vol, V. 



