Miseeltaneous. 89 
his subsequent generalizations of the value for systematic purposes 
of these two layers? The distinction of entoderm and ectoderm is, 
as Hiickel himself acknowledges, and as is sufficiently shown by 
Kowalevsky, of the greatest anatomical value ; yet how is it possible 
that these differently constructed Planule should have the genetic 
connexion claimed for them by Hiickel, if in their very embryonic 
stages the differences are of so radical a nature that, according to 
the very theory of embryonic layers so strongly insisted upon by 
Hiickel, they could have no possible relation, the one being a product 
of the entoderm, the other of the ectoderm, the two primitive em- 
bryonic layers ? 
It is not known, as is stated by Hiickel, that the walls of the 
primitive digestive cavity are invariably formed of the entoderm ; 
and when Hackel states the result (the Gastrula) to be the same 
whether formed by the ectoderm or entoderm, he states what is known 
to be exactly the contrary. Itis not known, as is stated by Hickel, 
that the mere fact of a Planula fixing itself by one extremity or not, 
will in one case lead to a radical type, in another to a bilateral 
type. What becomes of all the free-swimming embryos of Echi- 
noderms, of Acalephs, of Polyps? Are they bilateral? It is true 
Hackel is obliged, to suit his theory, to consider the Echinoderms as 
an aggregation of individuals ; but he has not the countenance of a 
single zoologist whose opinion on Echinoderms is of any value. 
When he says that Sars, whose knowledge of the development of 
Echinoderms was so accurate, agreed with his peculiar views, we 
can only reply that his agreement must be based upon a misunder- 
standing. We have equally as many radial and bilateral types 
developed either from fixed or from pelagic Gastrule; and to cite 
this as a causa efficiens, the mechanical reason of the genetic descent 
of all radiates from a fixed Gastrula, and of all bilateral types from 
a free-swimming one, is simply fantastic. How is it that so many 
Actiniz and Acalephs have their radiate structure developed long 
before they become fixed? It is not known that the embryonic 
layers of Acalephs are truly homologous to those of the higher 
Vertebrates. Huxley simply speaks of their bearing the same physio- 
logical relation to one another ; but until we know the Gustrula of 
other Vertebrates than Amphiowus it is idle to talk of the continuity 
existing between the ontogeny of Amphiowus and the remaining 
members of the Vertebrate branch, and to say that hence there is no 
_ doubt left that the ancestors of the Vertebrates must, in the 
beginning of their development, have passed through the Gastrula 
form! Neither Hiickel nor any one else has seen this; it is a 
pretty hint which may or may not be proved. 
Considerable confusion arises in Hiickel’s classification from his 
adopting at one time as of primary importance the development of 
the cavity of the body and making it the main point in his phylo- 
genetic classification, while previously the relations of the phylum to 
Protascus and Prothelmis (names he gives to the unknown ances- 
tors of the radial and bilateral types) formed the basis of his classi- 
fication. This places him in the awkward predicament of having a 
phylum of the animal kingdom (the radial) which has lost the 
