408 On Alternate Generation of Annelids, 



Fig. 11. — Fig. 10 seen in profile ; the last ring seems to 

 be divided into two, giving the figure the appearance of 

 an additional ring. 



Fig. 12. — Young parent stock of Autolytus, in which 

 bristles are developed at all the rings, and the tentacles of 

 the head somewhat more advanced than in fig. 9. 



Fig. 13. — First appearance of the tentacular cirrus C 

 which is developed after the dorsal cirri C" have been 

 formed on two or three rings, as seen in the next figure. 



Fig. 14. — The young parent stock of Autolytus has 

 all the appearance of a full-grown parent stock, having a 

 smaller number of rings, shorter tentacles, and smaller cirri. 



Fig. 15. — A more enlarged view of the head of a pa- 

 rent stock slightly older than that of fig. 14. 



Plate XI. 



Fig. 1. — The smaller tentacular cirri c"', the stiles 

 of the caudal ring and the appendages of all the rings 

 have been greatly developed since the stage represented 

 in PI. X. fig. 14. 



Fig. 2. — The number of rings is greatly increased, and 

 the cirri C and C specially have lengthened. 



Fig. 3. — Still more advanced individual. 



Fig. 4. — A view of the head of a full-grown parent 

 stock, seen from below, to show the mouth, M. 



Fig. 5. — The thirteen rings remaining of the parent 

 stock after the separation of the male or female individ- 

 ual, and the new rings formed since. 



Fig. 6. — Parent stock in which new rings have been 

 formed after the Autolytus has separated, and where the 

 eyes of a second individual are perceptible. 



Fig. 7. — The posterior extremity, in which the caudal 

 stiles are formed preparatory to the formation of new 

 rings, as in fig. 6. 



Fig. 8. — A male, seen from the lower side. The letters 



