82 PATTEN. [VoL. XII. 
For example, if fission progressed in Fig. 91 down to the 
abdominal region, leaving the newly formed abdominal ap- 
pendages as unpaired organs, just as the fourth appendage now 
is ; and if the anterior part of the right-hand embryo under- 
went median fusion and antero-posterior degeneration up to 
the fifth thoracic metamere, we would then have a condition 
like that in Fig. 99. I see little reason to doubt that the 
embryo in question was formed approximately in that way. 
2. TRIPLE EMBRYOS. 
Illustrations of triple embryos are seen in Figs. 102 to 104. 
The steps by which they were produced were probably as 
follows: It is assumed that in the beginning there was a 
single, normal embryo, and that it gave rise, by longitudinal 
fission, in the manner already described, to two embryos, each 
one composed of a new half and an old one, Fig. 7. The 
right-hand embryo then divides in the same way as the first, 
by the formation of two new halves, Fig. 10. The result 
is that the halves of the original embryo are now separated 
from each other by an angle of about 240°. The second 
embryo, &, is an entirely new formation, but embryo A con- 
sists of the original right half plus a new left half, and embryo C 
consists of the old left half plus a new right half. 
The original line of concrescence of the posterior margins of 
the mesodermic areas, 77.’ (along which the heart is formed ), 
remains unchanged, except in its position on the yolk, just as 
the original line of concrescence becomes the lower one in the 
double embryo. The other two heart lines, //z.?2 and “73, are 
entirely new formations. 
If we may speak of the new halves as separate genera- 
tions, their relations to each other in a triple embryo are 
as follows: In embryo A the body consists on the right 
side of the right half of a mother, and on the other of the 
left half of a daughter. Embryo 2B is composed on the right 
of the right half of a daughter, and on the left of the left 
half of a granddaughter. Embryo C is composed on the left 
side of the left half of a mother, and on the right side of the 
