Fig. 30. — Ti msvei ■> section through tail 

 : embryo belonging to the type illustrated 

 in PI. II. fig". 12 (ventral union by posterior 

 part 1 if body). There .in.- two spinal cords, 

 notochords, and dorsal edge membranes 

 Two ventral edge membranes ire also 

 present, but these are coiup 

 derived from the widely separated halves 

 of ventral membranes belonging to each 

 of the twins. This is an example of 

 almost pure ventral union. See pp. 22-23. 

 Compare with Fig. 31. (xi.f.) 



FlG. 1 I 1 section tin 



tail of an embryo belonging to the 

 general type illustrated in PI. VI. figs. 

 27-29. rhi two notocl fusi d 



together, and the ventral edge membrane 

 is composite and single. Compare with 

 Fig. 30. See also under Fig. 27. I 1 \.. 1 



Fig. 32 ; section through com- 



mencemi tail of the triple monster 



trout described on pp. 33-34 See also PI. 

 XXII. figs. 94-96 and PI. XXIII. figs 97-99. 

 The section is taken up chiefly with structures 

 belonging to the principal embryo, but it 

 shows also, near the middle line on the under 

 ■ i-l" 1 t . the two dorsal tins of the defective em- 

 bryos. A little further up on either side is a 

 composite ventral edge membrane (anal tin I. 

 belonging in part to the principal embryo and 

 inpart to one or othe! of the defective en ibrvo-.. 



(xi8.) 



Fig. 33. — Trans ■ ■ n thn >ugh 1 



pecimen as in last figure, but considerably 

 further back. All the fin membranes are stijl 

 present, but the two dorsals of the defective em- 

 bryos have almost united. The section, as well 

 as the succeeding one, may be compared with 

 Figs. 30 and 31. Other references under Fig. 32. 



• 



Fig. 34. — Transverse section as above. The 

 dorsal fins of the defective embryos have now 

 united. (xi8. ) 



PL. VII. 



