74 T. H. MORGAN. 



Fig. a. Phoxichilidium, 2-celled stage. 



Fig. b. Phoxichilidium, 4-celled stage. 



Fig. c. Phoxichilidium, 8-celled stage. 



Fig. d. Tanystylum orbiculare, 2-celled stage. 



Fig. e. Tanystylum orbiculare, 4-celled stage. 



Fig. f. Tanystylum orbiculare, 32 (?) -celled stage. 



Plate IV. 

 I-VIII, Pallene. IX, Tanystylum. 



Fig. I. Surface view of young embryo, to show anterior region. 



Fig. II. Surface view of ventral region of same. 



Fig. III. Ventral view of embryo with four pairs ventral ganglia, 

 first and second separate. 



Fig. IV. Dorsal view of embryo about same age (a little older 

 perhaps) as last. 



Fig. V. Ventral view of embryo. First and second ventral 

 ganglia have fused. 



Fig. VI. Side view of embryo, showing rudimentary abdomen 

 behind as a continuation of the body and in same plane as the body. 



Fig. VII. Ventral view of embryo at the age when it leaves the 

 parent. Fourth pair of walking legs seen behind; third pair of 

 appendages beginning just in front of first pair of walking legs. 



Fig. VIII. Dorsal view of last, to show brain and four eye spots. 

 In both VII and VIII only the proximal ends of the legs are shown. 



Fig. IX. The Pantopod-larva (Protonymphon of Hoek) of Tany- 

 stylum orbiculare. 



Plate V. — Metamorphosis of Tanystylum. Zeiss 4Ai 



Fig. X, stage 2. Young larva after leaving parent and after first (?) 

 moult. Ventral view. 



Fig. XI, stage 2. Dorsal view of last. 



Fig. XII, stage 3. Ventral view. 



Fig. XIII, stage 4. Ventral view, showing three pairs of ventral 

 ganglia, the first really composed of two. 



Fig. XIV, stage 4. Dorsal view of last. One pair of eyes — the 

 anterior. 



Fig. XV, stage 5. Ventral view with first pair of walking legs, 

 each with six segments. 



Fig. XVI, stage 6. Ventral view with two pairs walking legs, the 

 first with eight segments, the second with six. 



Fig. XVII, stage 7. Ventral view with three pairs walking legs, 



