406 On Alternate Generation of Annelids^ 



ing parts of the parent stock, and males or females are 

 marked by the same capital letter, A, A'' being the middle 

 tentacle and the right tentacle of the head ; C, C, C", C" 

 corresponding to c c' c" c'" in the figures of males and 

 females ; F and F', the anterior and posterior part of the 

 alimentary canal. 



Fig. 10. — Still more magnified view of the head of a 

 parent stock, letters as in fig. 9 ; M, the mouth ; B, the 

 eyes. 



Fig. 11. — The ring of the parent stock, in which the 

 tentacles of the head of the individual bearing the sex- 

 ual organs can be noticed as slight swellings, a, a' a". 



Fig. 12. — The same ring, showing the lateral tentacles 

 of the head {a' and a") somewhat more developed than in 

 the preceding figure. 



Fig. 13. — Somewhat more advanced; the large eyes 

 have made their appearance, and the long tentacular 

 cirrus {&) is seen behind the eye. 



Fig. 14. — The same as fig. 13 seen in profile, some- 

 what more advanced, as the small eye can be detected as 

 a minute spot above the large eye. 



Fig. 15. — The head at the time when the three tenta- 

 cles are equally developed ; the small eye has not yet made 

 its appearance, although the tentacles are more advanced 

 than in fig. 14. This is a male, while the preceding fig- 

 ures were probably females. 



Fiar- 1^- — Head of an individual which can with cer- 

 tainty be recognized as a female ; the tentacular cirri are 

 very small, c, c'. 



Fig. 17. — The head of a male previous to the time 

 when the tentacles begin to fork ; the tentacle a is gener- 

 ally turned towards the tail in the males, and carried 

 straight forward in the females. 



Fig. 18. — Head of a female just before it is ready to 

 separate from the parent stock. 



