28 



EARTHWORMS AND LEECHES 



[CH. I 



passes. Opportunities for a full meal occurring but inter- 

 mittently, it is all important that 

 the leech should be able to avail 

 itself to the utmost of the rare 

 occasion and lay up a store that 

 will last for a considerable time. 

 A well-fed Medicinal Leech, now 

 but rarely found in this country, 

 is said to be able to fast for 

 some nine months. In this 

 species the stomach is very 

 small, and the intestine though 

 straight contains a closely coiled 

 spiral valve down which the 

 food but slowly winds its way 

 to the anus. The common 

 Horseleech (Aulostoma) does 

 not as a matter of fact suck the 

 blood of vertebrates, having but 



Fig. 6. View of the internal organs of 



Hirudo medicinalis. On the left 



side the alimentary canal is shown, 



but the right half of this organ has 



been removed to show the excretory 



and reproductive organs. 

 1. Head with eye spots. 2. Muscular 



pharynx. 3. 1st diverticulum of 



the crop. 4. llth diverticnlum of 



the crop. 5. Stomach. 6. Eectum. 



7. Anus. 8. Cerebral ganglia. 



9. Ventral nerve-cord. 10. Nephri- 



dium. 11. Lateral blood vessel. 



12. Testis. 13. Vas deferens. 



14. Prostate. 15. Penis. 16. Ovary. 



17. Uterus a dilatation formed by j?ig 6 



the conjoined oviducts. 



