SUMMARY OF CONTENTS OF PLATES. 



Pis. XVII.-XXI. figs. 56-93, PI. XXII. figs. 94-96, PI. XXIV. figs. 100-106, are from drawings made 

 by the author, and are based on the study of numerous series of sections. All the other plates and figures 

 are from photomicrographs of specimens or sections. 



Pis. I. -II. figs. 1-12. 



Surface views of normal trout embryo, and of specimens 

 belonging to various Classes of double monstrosity. 



Pis. III.-IV. figs. 13-20 ; also PI. VI. figs. 24-26. 



Transverse sections of a normal trout embryo at the same 

 stage in development as the monstrosities described. 

 Compare with the sections, etc., of the latter, shown in 

 the succeeding Plates. 



PI. V. figs. 21-23. 



Horizontal sections of normal trout embryo, as above. 



PI. VI. figs. 27-29 ; also PI. VII. figs. 30-31. 



Transverse sections of double monsters with union in the 

 posterior part of the body (Class VI. (a) and (b) ). 



PI. VII. figs. 32-34. 



Transverse sections through the triple monster described 

 on pp. 33-34 ; see also Pis. XXII.-XXIII. figs. 94-99. 



Pis. VIII. -IX. figs. 35-38. 



Transverse section through the head of a double monster 

 with union of the twin brains in the region of the optic 

 lobes (Class I.). 



Pis. X.-XI. figs. 39-42. 



Horizontal section through the head of a double monster 

 with union of the twin brains in the region of the optic 

 lobes (Class I.). 



PI. XII. figs. 43-46. 



Horizontal sections, as above, but in a specimen showing 

 a different disposition of various parts. 



Pis. XIII.-XIV. figs. 47-51. 



Transverse sections through the head of a double monster 

 with union of the twin brains in the region of the medulla 

 (Class II.). 



Pis. XV.-XVI. figs. 52-55. 



Horizontal sections of a double monster with union in 

 the pectoral region, inner pectoral fins not being present 

 (Class III.). 



PI. XVII. figs. 56-63. 



Diagrams to illustrate : the cartilaginous cranial, hyo- 

 mandibular, and vertebral, skeletal elements in normal 

 trout embryos, and in double monsters belonging to 

 Classes I. and II. (union of the twin brains in the region 

 of the optic lobes or of the medulla). 



PI. XVIII. figs. 64-72. 



Figs. 64 and 65 illustrate the visceral arch cartilages, and 

 Figs. 67 and 68 the vascular system in double .monsters 

 belonging to Classes I. and II. Fig. 66 shows the inner 



girdle and fin cartilages in an example from Class IV. 

 (union in pectoral region, inner pectoral fins being present 

 but united). Figs. 69-72 are diagrams to illustrate the 

 cavities of the brain in a normal embryo and in double 

 monsters belonging to Classes I. and II. 



PI. XIX. figs. 73-81. 



Figs. 73-75 illustrate the heart in a normal embryo and 

 in double monsters belonging to Class III. (union in 

 pectoral region, adjacent pectoral fins not being repre- 

 sented) and Class iV. (union in pectoral region, adjacent 

 pectoral fins being present but united). Figs. 76-81 

 illustrate the posterior ends of the Wolffian ducts, the 

 bladders and urinary pores in a normal embryo and in 

 double monsters belonging to Classes V. and Vl. (union 

 by the body or tail). 



PI. XX. figs. 82-87. 



Fig. 82 shows the inner composite otocyst in a double 

 monster belonging to Class II. (union of the twin brains 

 at the medulla). Figs. 83-87 illustrate the glomerulus 

 and the head-kidney and the first portions of the Wolffian 

 ducts in normal embryos and in specimens belonging to 

 Classes I. II. III. and IV. of double monstrosity. 



PI. XXI. figs. 88-93. 



Diagrams with transverse lines to indicate the planes 

 and levels of certain typical sections of which photo- 

 micrographs are shown in the earlier plates. The struc- 

 tures particularly illustrated are the brain cavities and 

 the cranial and hyomandibular skeleton. 



PI. XXII. figs. 94-96. 



These figures illustrate the external appearance and the 

 alimentary and urinary structures of the triple monster 

 described on pp. 33, 34. 



PL XXIII. figs. 97-99. 



Transverse sections of the body of the triple monster ; 

 see also PI. VII. figs. 32-34. 



PI. XXIV. figs. 100-106. 



The figures illustrate cyclopia (pp. 40-45) and super- 

 numerary eyes (pp. 59, 60). 



PI. XXV. figs. 107-110. 



Transverse sections through the ocular region in cyclopia 

 and sera icy clopia (p. 44). 



PI. XXVI. figs. 111-114. 



Fig. Ill follows Fig. 110 in illustrating semicyclopia ; 

 Fig. 112 shows the atrophic head referred to on p. 61 ; 

 Fig. 113 is a seotion showing absence of notochord ; and 

 Fig. 114 a section behind the pectoral fins in a double 

 monster belonging to Class IV. 



