84 (PAIL: [VoOE.Zon: 
lengthwise in the manner already described, producing A and 
BC, and that BC divided, giving rise to Band C. In Fig. 102 
A remains practically normal ; 4 has undergone median fusion 
and transverse fission across the line of the fourth segment. 
The abdomen and last two thoracic appendages are practically 
normal, while the anterior part of the thorax and cephalic lobes 
have disappeared, except one pair of fused appendages. 
Passing around to embryo C, we find median fusion and degen- 
eration have obliterated everything but the abdomen and the 
last pair of fused thoracic appendages. 
In Fig. 103, 4 has undergone median fusion and degenera- 
tion, forming a pretty good example of an hour-glass embryo. 
The same process has affected 4, obliterating entirely the 
cephalic lobes and anterior portion of the thorax. The dorsal 
organs, however, are not quite fused in the median line. But 
this has taken place:in C, and in other respects the degenera- 
tion is carried farther than in &. In both these triple embryos, 
then, the path of increasing degeneration ts that of a spiral 
from A to C.} 
In Fig. 104 all three embryos are reduced so nearly to the 
same level that it is hard to determine which is the most de- 
generate. They are reduced to the last two fused thoracic 
appendages and a remnant of the abdomen. Embryo C has the 
smallest appendages and may be taken to be the most degener- 
ate. But between A and BZ there is so little distinction that one 
cannot determine whether the line of degeneration follows a 
right or a left handed spiral. We shall return to this point later. 
Discussion of Observations on Defective and Exuberant Em- 
bryos. — There is little hope in the present condition of our 
knowledge of finding anything like a satisfactory explanation 
of the phenomena of either defective or exuberant embryos, be- 
cause the solution of the problem is bound up in that of vitality. 
While the futility of seeking final explanations of vital pheno- 
mena is fully recognized, we have ventured, supported by the 
facts on variation here described, to approach some of the out- 
posts of the subject. These facts are numerous and in some 
1 Possibly, from C to 4, as more recent evidence indicates. 
