20 
PATTEN. [Vou. XII. 
Pace 
Internal differential tension due to movement of the embryo over 
the yolk has no effect on the shape of organs..........-2-2...:-00-+ 76 
Causes influencing complete separation from each other of double 
TINE Ty, OS! Serene cera cones aaa ne ae eae cane genera rere ee oa ne hte rane ene 77 
Formation of new embryos by excessive growth, followed imme- 
diately, or accompanied, by degeneration = see ere eee 80-81 
2. Triple Embryos. 
Due to addition of four new halves to the old embryo.............2...0..... 82 
Relation ‘of newihalves)to) Oldies tse nee essere cree secre eo ce 83 
Mother, daughter, and granddaughter hearts. ................:::-eesceccceeceeee-os 83 
Difference in age of the individuals in triplets is not primary cause 
of their difference in degeneration. 
Discussion of observations on defective and exuberant embryos.... 84-88 
Various classes of facts and explanations to be harmonized before 
we can arrive at any explanation of the phenomena observed in 
triple embryos, viz. : 
(1) There is variation in the duration of the growth period of the 
whole, or of a part of the organism. We may assume this to be 
due to variations in the intensity of growth, or differentiation, 
forces; but not to the lack of formative material. 
(2) There may be an entire absence of certain organs at the outset 
and a subsequent failure to regenerate the same. This we may 
assume is due to absence of specific formative material. 
(3) General or local structural weakness of an embryo is indicated 
by median fusion of its organs in the reverse order of their age 
and specialization. 
(4) The existence of abnormally large embryos may indicate forced 
growth or an excess of formative material. Multiple embryos 
may be explained in the same way. In either case excess of 
material or excessive growth gives rise to the formation of new 
organs in reverse order of that in which they disappeared by 
median fusion and degeneration. 
(5) When the formation of new organs is followed by degeneration, 
we assume that the multiple parts are formed not from an excess 
of formative material, but by a kind of forced growth obtained 
by drawing from a fixed capital. 
(6) The same explanation must apply to the cases where the indi- 
viduals of triple embryos are at first very dissimilar, but finally 
before their complete degeneration become equal in size and 
structure. 
No production of new formative material by abnormal environment, 
Multiple embryos probably due to abnormally rapid, or forced, growth. 
New organs in multiple embryos are formed at point of greatest 
differentiation tension ............... ES OTT She ane oor mee Le LS 89 
Comparison of recuperation of weaker part from stronger, in multiple 
embryos, and absence of same in single embryos.........-.-.-..------0--+-++ go 
Explanation of more frequent presence of asymmetry at posterior 
end of, body than at anterior. .....2¢ =: -0 eee ee go 
