EOSACETTS, FIACK (COMATULA EOSACEA OF LAMAECK). 
533 
temporary, yet partaking during their life, of the life of the embryo, and as affording ho 
evidence of possessing independent vitality. I imagine that as the term Embryo has not 
been applied to the yelk, or to the germ-mass before the separation of the organs of the 
young, it would be a like misapplication of the term to apply it to any stage in the 
development from that germ-mass of a being whose organs do not homologate with, and 
never by any subsequent metamorphosis become converted into, the analogous organs of 
the perfect form. Again, according to the ordinary conception of a “ larva,” it is a stage 
in the development of an animal during which its external form differs to a greater or 
less degree from that of the “imago” or mature form, and its organs are greatly modi- 
fied for the performance of certain functions at the expense of others ; but the organs 
of the larva are essentially the organs of the imago ; and the individual which is formed 
of the sum of these organs, and which manifests vital phenomena, is the same individual 
which subsequently lives as the imago. It is utterly inconceivable that the larva and 
the imago should exist as separate individuals at the same time. The relations of the 
pseudembryo are entirely different. It is developed from the germ-mass as a distinct 
animal form, manifesting a combination of vital phenomena, through a sum of organs 
which attain a distinct maturity of their own, and which never pass in combination into 
the sum of the organs of the perfect being. So complete is this independence, that in 
cases where this type of the reproductive process is carried out most fully, as in Bipin- 
naria, the embryo is at a certain period cast off from the pseudembryo, and both beings 
continue for some time to manifest independent life. I would therefore define a 
“pseudembryo” or a “ pseudembryonic appendage” as any provisional appendage pro- 
duced from the germ-mass, which manifests the functions of organic and animal life 
through the medium of a combination of organs which precede and do not homologate 
with the organs of the true embryo. This appendage may be reduced to a condition of 
extreme simplicity. It may exist merely as a layer of structureless sarcode, ciliated, 
and manifesting the form of life characteristic of the simpler Protozoa ; within which 
the organs of the embryo are gradually built up. 
In most, however, if not in all the invertebrate groups, the so-called embryo differs 
greatly in external form from the mature organism. 
It usually commences in aquatic animals as a “ ciliated germ ” ; and in this condition, 
whether within the vitelline sac or free after the rupture of the sac, it increases in size 
by absorption through the general surface. Very usually various lobes and fringes are 
produced, frequently richly ciliated, extensions of a transparent sarcodic investing layer, 
within which — but bearing to it only obscure relations in form — the nascent organs of the 
true embryo are slowly differentiated. During this period the permanent organs, so far 
as their special functions are concerned, are utterly inert. They are merely growing. 
The rudiments of the alimentary canal are being laid down, but probably the mouth 
has not yet “broken through.” The entire zooid, however, is by no means inactive. 
It moves rapidly through the water, its movements beautifully characteristic, and appa- 
rently guided by an obstruction-perceiving and light-perceiving instinct. 
