FIG. i. Side view of a normal trout embryo of same age as> the 

 monsters described. Seclions of similar normal specimens are 

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

 verse); and in PI. V. fig?. 21-23 (horizontal). Diagrams of skeleton, 

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

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

 (X 3 .) 



FIG. 4. View from above of a double monster belonging to 

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

 lobes. Transverse sections of a. similar specimen are shown in 

 Pis. VI 1 1. -IX., figs. 35-38, horizontal sections in Pis. X.-XII. 

 figs. 39-46, and diagrams of cranial skeleton, etc., in PI. XVI I. 

 figs. 58, 59 ; XVI II. figs. 64, 67, 70, 72. Description under Class I. 

 on pp. 12-15. (><3-) 



FIG. 2. Side view of a double trout embryo, w ith 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 Meckelian bars. 

 For references, see under Fig. 4. ( x 3.) 



FIG. 3. -Side view of a specimen similar to the last, but with one 



See pp. 7, 44. 

 sections of this 



"*-> ,} .^Illt. *n_v Ul tl afdlUldl J'""1<4I V 1 -" UIC ill 



of the heads showing a condition of semi-cyclopia. See pp. 7, 44. 

 Figs. 109-111, in Pis. XXV.-XXVI., are from 



specimen. (x3.) 



FIG. 6. View from below of a double monster belonging to 

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

 medulla oblongata. The two adjacent eyes are seen ; also the two 

 mouth-openings, separated by a thick septum containing the 

 adjacent hyomandibular and Meckelian cartilages. Sections are 

 shown in PI. XIII. figs. 47, 48, and XIV. figs. 49-51. Diagrams of 

 cranial skeleton, etc., in PI. XVII. figs. 60, 61, XVIII. figs. 65, 68. 

 71. Description under Class II. on pp. 15-18. (X3.) 



PL. I. 



