Fig. i. Side view ol a n .il trout embryo of same age .i 3 the 



monsters described. Sections ol similar normal specimens are 

 shown in PI. III. riys 13-16, IV. figs. 17-20, VI figs. 24-26 (trans- 

 and in PI. V. figs. 21-23 1 Diagrams of skeleton, 



etc. in PI. XVII. Rrs. 56, 57, 62, Will fig. 69, XIX. figs. 73, 76. 

 XX. fig. 83. Description on pp. 11 12. Contrast with Figs. 2-12. 

 I I 1 



1'h,. 4.— View in. in above ol a double : >" l " 



Class I., i.e. with union of the twin brains in the region of the optic 

 i 1 .Transverse sections of a similar specimen are shown in 



P VIII. -IX., figs. 3$-s&. horizontal sections in Pis. X.-XI1 

 figs. 39-46, ami diagrams ol ci i eleton, etc., in PI. XVII. 



figs.58,59; XVIII. figs. 64, 67, 70, 72. Descripl i I 



on pp. 1 2- is. ( 



-Side view of a double trout embryo, with union by the 

 yolk-sac only. See pp. 23-24. ( x 3.) 



Fig. 5. — View from ventral aspect of the double monster illus- 

 trated in Fig. 4. Two mouth-openings are seen, separated by a 

 septum containing the remains of the adjacent Mei I 

 For references, see under Fig. 4. ( X3.) 



Fig. 3 S ■ ew o( a specimen simitar t" the last, but v> 

 of the I See pp. 7, 44. 



Figs. 109-111, in Pis. XXV.-XXVI., arc from sections of this 

 specimen. ( X3.) 



FlG. 6. View from below of a double monster belonging t<> 

 Class II., i.e. with union of the twin brains in the region of the 

 medulla oblongata. The two adjacent eyi ; also the two 



mouth-op* mings, separated by 1 thick septum containing the 

 adjacent hyomandibular and Meckelian cartilages. S 

 shown in PI. XIII. iigs. 47, 4:-;, and XIV. figs. 49-51. Diagrams of 

 cranial skeleton, etc., in I'l. XVII. tigs. 60, 61. XVI II. figs. 65,68. 

 71. Descripl ' 1 Kiss II. on pp. 15-18. ' 



PI.. 



