JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATION OF PLATE XXV, 



Illustrating Professor Lankester's '' Notes ou Embryology 

 aud Classificatiou." 



A. Anus. 

 Jr. Arcliitroch. 

 Br. Branchiotrocb. 

 Ce. Cephalotroch. 

 Ep. Epitrocb. 



F. Foot. 



G. F. Gill-filaments. 

 Lb. Labial tentacles. 

 M. Mouth. 



Shg. Shell-gland. 



The dotted band represents the cephalic, the black band the branchial 

 portion of the architroch. 



¥iG. 1. — Hypothetical telostomiate organism, with primitive axis and 

 circular architroch. Ar. 



Fig. 2.— Hypothetical prostomiate organism, with secondary axis and 

 shifted architroch. Ar. 



Fig. 3. — Architrochic Echinoderm larva (after Gegenbaur). 



Fig. 4. — Zygotrochic Echinoderm larva (after Gegeiibaur). 



Fig. 5. — Front view of zygotrochic Echinoderm larva. 



Fig. 6. — Cephalotrochic larva (of Ciisetopod, Nemertine, or Gastropod 

 Mollusc), the so-called " Trochosphere." 



Fig. 7. — "Pluteus" larva of Echinids and Ophinrids (architrochic, ane- 

 pitrochic). 



Fig. 8. — "Tornaria" larva of Balanoglossus (zygotrochic, epitrochic). 



Fig. 9. — " Auricularia" larva of Holothurian (architrochic, anepitrochic). 



Fig. 10. — Transition form of the architrochic Auricularia, leading to the 

 " vermiform " Jarva. 



Fig. 11. — Vermiform Holothurian larva (zygotrochic, polyepitrochic). 



Fig. 12. — "Bracliiolaria" larva of Asterids (zygotrochic, anepitrocliic). 



Fig. 13. — "Actinotrocha" larva of the Gephyrsean Phoronis (architrochic, 

 epitrochic, with deficient development of tlie cephalic portion of the 

 arcliitroch). 



Fig. 14. — Lateral view of the same larva. 



Fig. 15. — " Veliger" larva of Gasteropod, with filamentary cephalotroch 

 comparable to the tentacles of Polyzoa (cephalotrochic, anepitrochic). 



Fig. 16. — Diagram of a Lamellibranch Mollusc, seen from the ventral 

 surface (architrochic, with conversion of the cephalic portion of the archi- 

 troch into labial tentacles and of the branchial portion into gill-filaments). 



Fig. 17. — Diagram of a Tentaculibranoh Mollusc (Polyzoon), seen from 

 the ventral surface (architrochic, anepitrochic). 



Fig. 18. — Hypotiietical mollusc with filamentous architroch, foot, and 

 shell-gland. 



Fig. 19. — Diagram of a Pot iter, with tentaculiferous cephalotroch. 



Fig. 20. — Diagram of a Polyzoon, with circular tentaculiferous archi- 

 troch. 



