288 



MOLLUSCA 



[CH. 



Internal 

 structure. 



12 



for into it the excretory organ opens and in the embryo 

 the genital cells are budded from its wall. Other large spaces 

 existing in the head and neck have no connection with the 

 coelom but are really parts of the blood system. Since there are 

 no regular veins, except those which run in the mantle-roof, the 

 arteries open into irregular spaces. It will be remembered that the 

 space called pericardium amongst the Arthropods is really a 

 blood space and that the heart opens into it by 

 openings called ostia : the coelomic character of the 

 pericardium of Mollusca is then another distinguishing 



feature of the group. It 

 opens by a narrow ciliated 

 passage, the reno-peri- 

 cardial canal, into the 

 kidney, which is seen in 

 the mantle-roof beside the 

 pericardium (5, Fig. 128). 

 The kidney looks like a 

 solid yellow organ ; but in 

 reality it is a vesicle into 

 the cavity of which nu- 

 merous folds project, cover- 

 ed by the peculiar cells 

 which have the power of 

 8 extracting waste products 

 from the blood, which flows 

 in spaces in the kidney 

 wall. The kidney com- 

 municates with the exterior 

 by a narrow thin-walled 

 tube, the ureter, which 

 runs along the right side 

 of the body and opens on 

 the lip of the respiratory 

 FIG 129. Helix pomatia, with the supper wall opening, just above the 

 of the pulmonary chamber cut open and 

 folded back. From Hatschek and Cori. opening of the anus (10, 



1. Ventricle. 2. Anterior tentacles. 3. Eye Fig. 131). 



tentacles.* 4. Cut edge of mantle. Thp kirlnpvi'n Molina 



5. Kespiratory pore. 6. Anus. 7. Open- 



ing of ureter. 8. Foot. 9. Auricle varies a good deal in struc- 



receiving pulmonary vein. 10. Eectum. 



11. Kidney. 



10- 



4 



pulmonary chamber. 



ven. . ecum. t u f ,]. U - lf 



12. Upper wall of ire ' 



on the same fundamental 



