of a few Annelids, 255 



EXPLANATION OF PLATES V. & VL 



V, anterior vibratile ring, t, tentacles. 



»', anal vibratile ring. y, concretion capsules. 



m, mouth. a, anus. 



e, eye-specks. rg, fifth ring in Polydora. 



0, oesophagus. r, first ring; the rings are counted from here. 



s, stomach. g, glands of Polydora. 



c, intestine. 



Plate V. 



Fig. 1. Young Planaria angulata, with distinct articulations, seen from 

 above. 



Fig. 2. Somewhat older than fig. 1 ; both figures greatly magnified. 



Fig. 3. Youngest stage of Nareda observed ; seen in profile. 



Fig. 4. Somewhat more advanced than fig. 3; the pigment-spots have 

 increased in number, the tentacles of the head are making their 

 appearance : seen in profile. 



Fig. 5. Older stage, in which the difference in width between the anterior 

 disk and the body has attained its maximum ; large increase in 

 number of pigment-spots, diminution in diameter of digestive 

 cavity : seen in profile. 



Fig. 6. Posterior extremity of young Nareda, about in the condition of 

 fig. 5, showing the intestine and place of formation of new rings; 

 seen in profile. 



Fig. 7' Stage in which the anterior disk is diminishing in size and be- 

 coming slightly elongated ; seen from the dorsal side. 



Fig. 8. Head of Nareda in stage of fig. 7 : seen from the mouth side. 



Fig. d. Older stage than fig. 8 ; the rings are further apart, the pigment- 

 spots larger; the head has become greatly elongated, and the 

 tentacles are more prominent : seen from the dorsal side. 



Fig. 10. Older than fig. 9; the pigment-spots have become quite small, 

 and the vibratile rings are much reduced : seen from the dorsal 

 side. 



Fig. 11. Somewhat more advanced than fig. 10; the anterior disk has lost 

 its prominence, the vibratile cilia have nearly disappeared, the 

 stomach has become convoluted, the pigment-spots are scarcely 

 perceptible, and the articulations quite indistinct : seen in pro- 

 file : very sluggish in its movements; about one-fourth of an 

 inch long. 



Fig. 12. Head of specimen slightly older than fig. 11 ; seen in profile. 



Fig. 13. The same, seen from the dorsal side; the tentacles are con- 

 tracting. 



Fig. 14. Young Nareda which has lost almost all trace of the tentacles of 

 the head, about half an inch long. 



Fig. \5. Head of a somewhat older specimen. 



Fig. 16. The same as fig. 15; seen in profile. 



Fig. 17. The head of a Nareda which has become less wide than the 

 body ; about five months older than fig. 4. 



Fig. 18. Portion of string of ej^gs of Spirorbis. 



Fig. ly. Young Terebella fulgiaa, Ag., showing the order of development 

 of the tentacles, t^, t^, and the concretionary lime capsules, y; 

 greatly magnified. 



Fig. 19^. Stiff* bristles of the rings ; magnified. 



