:^^o'»» "^y 



f^/^ -%►#-*. <^<f^ 



LIBRARY 



^>'^.f3>^CY 



/;/ — 

 LIST OF ILLUSTRATIONS ^^^^ 



PAGE 



Figs. 1-3. Various Types of Twin Larvae of Patiria . . 17 



Figs. 4-6. Common Types of Symmetrical Twin Larvae of 



Patiria 18 



Figs. 7, 8. Two Advanced Larvae of Patiria 19 



Figs. 9-14. Types of Blastulae and Gastrulae of Patiria . 20 



Figs. 15-17. Types of Starfish Anadidymi 24 



Figs. 18-21. Four Stages in the Transformation of a Twin 



Patiria Larva into a Single Larva ... 26 



Fig. 22. Typical Twin Earthworm, Allolohophora sub- 



ruhicunda 32 



Figs. 23, 24. Germ-Ring Stages of Trout Twins ... 41 



Figs. 25, 26. Autosite-Parasite T)^es of Trout Double 



Monsters 47 



Figs. 27, 28. Typical "Separate" Twins of Trout ... 48 



Figs. 29-31. Various Types of Trout Anadidymi ... 54 



Figs. 32, 2)Z- Diagrams Showing Mode of Embryo Forma- 

 tion in Fishes 58 



Figs. 34. Triplet Chick Embryo (after Dareste) .... 77 

 Fig. 35. Early Stage of Twinning in Chick Derived from 



Fission of the Blastoderm 78 



Fig. :i,6. Chick Twins Resulting from Double Gastrulation 79 



Fig. 37. Chick Double Monster Due to Head-on Collision 



and Fusion 80 



Fig. 38. Chick Double Monster Due to Fusion of Two Head 



Ends 81 



Fig. 39. Triplet Chick Embryo (after Dareste) .... 82 



Fig. 40. T)rpical Chick Anadidymus 83 



Fig. 41. Typical Chick Katadidymus 84 



Fig. 42. Rare Type of Chick Twin Resulting from Nearly 

 Complete Longitudinal Fission of a Single 



Embryonic Axis 86 



xi 



