24 
for it was not until after my paper had been read that a first study 
of the Echinoderm memoirs convinced me how nearly he had antici- 
pated what follows. 
Before passing to the subject one further remark may be per- 
missible. Owing to lack of time when reading the paper no oppor- 
tunity offered itself for pointing out the analogy which would obtain 
between the suggested mode of Metazoan development and the accepted 
fact of an alternation of generations in the life-histories of all plants 
above the lowest Thallophytes. 
Furthermore nothing was said about the mode of formation of 
the “mesoderm” in certain cases as one or more outgrowths of the 
endoderm; although the writer was fully alive to the explanation 
which from his standpoint could be offered. This and other questions 
of a like character would receive consideration in the complete 
paper, in which it would be insisted that such things and processes 
nead be neither “palingenetic” nor “coenogenetic”, but that the ana- 
logy of the formation of imaginal discs in Insecta, or in the Pili- 
dium of the Nermertine, ought to suffice to account for them. 
As an instance, the formation of the mesoblastic somites in Am- 
phioxus may be only a mode in which certain parts of the adult 
are in that particular case laid down upon the larva. 
And now, after this digression, to return to the question under 
consideration. Two modes of development have long been distinguished, 
viz: — larval with metamorphosis, and foetal and direct. 
Cases are known in which there subsists no homology between the 
larva and the adult, and even such in which the larva (Bipinnaria 
asterigera) is said to exist apart for a time after it has given rise 
to the Echinoderm. In many such, moreover, the sole larval organ 
carried over to the adult is the alimentary tract, all other organs of 
the larva, such as nervous system, sense organs, locomotor and ex- 
cretory organs, mouth and anus &c., being replaced by new formations 
n the adult. The new organs are thus not homologous with those of 
the larva: indeed, neither as a whole, nor in its parts, is the larva 
the homologue of the adult form, but the latter arises upon the former 
by a mode of asexual generation. 
The birth of the Nemertine on the Pilidium, and that of the 
Echinoderm on the Pluteus, or upon the Bipinnaria asteri- 
gera, may be cited as examples, and the question may now be asked 
“what becomes of the larva when «) food yolk is acquired, and £) 
when uterine development is initiated ?” 
Does the larva really disappear? Anticipating the sequel, it is 
asserted that the larva never vanishes from the development, but is 
