50 ATLAS OF BIOLOGY. 



FIG. IX. Enlarged drawing of the left half of somite XV., after removal of the crop 

 specially to show the position and segments of the excretory organ. The loop marked * 

 is ciliated, x 25. 



lu order to make out the natural relations of the excretory organ, it is advisable to 

 preserve the animal in alcohol for a day or two, prior to dissecting. 



FIG. X. Terminal left-hand portion of Fig. IX. magnified, the looped blood-vessels of 

 one side being indicated. D. 3. 



These vessels usually bear numerous knotted appendages [see Lankester (48) and 

 Claparede (42)]. They are often, as in the specimen here figured, wholly absent. D. 3. 



FIG. XI. A portion of the same, viewed in optical section. D. 3. 



FIG. XII. The mouth of the excretory organ. D. 3. 



This can only be removed from the 'body, together with a portion of the mesentery 

 which it perforates. 



The whole structure of the Earthworm's excretory organ has been most successfully 

 worked out by Gegenbaur (44), and Claparede (42). 



f 



FIG. XIII.- Dissection from the left side, showing especially the alimentary canal in 

 section, and incidentally, the nervous system and genital organs, x 2^. 



Eighteen hours' previous immersion in alcohol is here necessary, in order that the parts 

 may be well set in their natural positions. 



Of the cesophageal glands the two hinder pairs are always smaller than the one in front, 

 and their apertures are sometimes obliterated (see Fig. VIII.) 



