No. 420.] REGENERATION IN THE EGG. 963 
may also appear in the middle of the plate if the middle comes 
to represent the anterior end, as is the case in the experiment 
just described. 
A most important theoretical question is involved in these 
results, although it has not been as yet sufficiently considered 
by those who have carried out the experiments, vig., that a stage 
once passed through by the embryo cannot be repeated again 
by the other parts of the body that may not have been directly 
concerned in the operation, although these parts possessed 
this power at an earlier stage. A thorough discussion of this 
important question would lead us too far from our present sub- 
ject, but I may point out that the result indicates that at each 
stage in the development the ultimate structure seems to change 
its organization, so that it no longer repeats a stage once com- 
pleted. The organism has not, however, lost the power of form- 
ing a new individual, or at least certain parts have not, since 
eges are produced by the adult animal, each of which may make 
an entire organism, and the adult animal has also the power in 
many cases of replacing lost parts, although it does not repeat 
the embryonic processes in doing 50. i 
When we examine the method of development of pieces of 
still later stages of the embryo we find the process more and 
more like that which takes place in the adult. In the higher 
forms (echinoderms, mollusks, annelids, and vertebrates) the 
regeneration of the late stages of the 
the adult takes place by the developmen 
free end, while in the earlier stages in certain embryos in these 
groups a new whole is established by the entire structure 
changing aver into the new form. In other words, the method 
of development of pieces of the early embryo 15 Ee that to- 
lowed by the lower animals, j.e., by a process of morphallaxis, 
he method of regen- 
While in the later stages of development t 
eration is more like that in the higher animals. scs 
seems to be connected with what we call the spec! agen 
u 
the tissues in the later stages of development and in Ud T ¥ 
of the higher forms, but what is meant by this specta ing "e x 
a question that needs to be further examined, although it wi 
not be possible to do so at the prac en’ 
E 
