874 Values of the Stages of Growth and Decline. 
istic of the larger divisions of the Animal Kingdom, would not, if 
arrested at this period, be recognized as belonging to the same groups 
as their existing adults. They do not possess, as a rule, the essen- 
tial diagnostic characters of the larger divisions to which they 
belong, and we propose to call them Neoembryos. Examples: the 
Cinctoplanula is not a sponge, the Planula of the Coelenterata is not a 
Ccelenterate, nor the Pluteus an Echinoderm, nor the Trochosphere 
a Mollusc, nor the Pilidium a Nemertean worm, nor the earliest 
planula-like ciliated stages of Amphioxus a Vertebrate. Neoem- 
bryos are, as pointed out by Semper,! Lankester ? and Balfour,’ so 
similar, that they may be considered as indicating a common 
ancestor for the entire Animal Kingdom. 
(7) The latest of the more specialized planula-like stages are 
either directly transformed into, or else give rise to other forms in 
which the characters of the larger subdivisions or types of the Animal 
Kingdom begin to appear, at least so far as essential characters are 
concerned. Examples: the Ascula and Ampullinula are true 
sponges, the Actinula isa Hydrozoon, the Gulinula is an Actinozoon, 
the Veliger is a Molluse, the internal worm-like form arising in 
Pilidium is a true Nemertean, the formation of the notochord in 
Amphioxus makes the planula-like embryo into a vertebrate animal. 
They have the essential characters of the larger subdivisions, though 
it is equally true, that embryos in this stage of development are 
very remote, in some cases, from the adults of any normal forms. 
We do not, therefore, misinterpret these relations by naming the 
embryo in these last stages the Typembryo. This term can 
applied to the Nauplius of Crustacea, and the Echinula* of Echino- 
dermata, as well as to those above noted. 
1 Semper, Stammsver, Wirbel. und Wirbello., Arbeit. Zoolog. Zootom 
Inst., V. ii., p. 59, and V. iii., p. 384. This distinguished author states 
in Volume iii., that his “ Trochosphaera”’ is identical with the “ unge- 
gliderte Urnierenthier”’ which in his first table in Volume ii., app 
as the common ancestor of the higher animals, i.e., of all animals except 
Echinodermata and Coelenterata. 
2 Lankester traced the Mollusca, Annelida, Rotifera and Echinoder- 
mata to what he calls the Archiiroch, acomimon form taken from some 
what earlier stages of the Planula than those selected by Semper for his 
rochosphaera. Embryol. and Classif. Journ. Micros. Sci., vol. vile 
1877, p. 423. 
* Balfour, Comp. Embryol., vol. ii., p. 811. 
t Alexander Agassiz, Address, Am. Ass. Adv. Sci., V. 29, 1880, p. 410, 
shows that there is a stage of the embryo common to all orders of living 
