~ 
474 Scientific Intelligence. 
ancestors of the Vertebrates must have passed through in the 
beginning of their development the gastrula form! Neither 
zckel nor any one else has seen this; it is a pretty hint which 
may or may not be proved. 
“ Considerable confixion arises in Heeckel’s classification from his 
adopting at one time as of primary importance the development 
of the cavity of the body nea making it the main point in his 
phylogenetic classification, while pen y. the relations of bes 
Protascus and Prothelmis (names he gives to the un- 
known ancestors of the radial and bilateral pe) formed the bon 
of his classification. This places him in the awkward predicament 
of having a phylum of the animal kingdom (the radial) which has 
it the capacity of forming a body cavity, and yet its descendants 
ve in some unaccountable manner (entirely against the rules of 
Heckel’ theory) managed to get one by some unexplained 
method. We do not see how it can be so confidently stated by 
Heckel that Echinoderms have lost their engine central nervous 
organ; there is no proof whatever of its aving existed 
There is, as yet, no proof whatever that the organs of sense (which, 
as had already been so often insisted upon by Agassiz, are not 
e 
the same phylogenetic origin. When Heckel says that the 
mouth of Echinoderms is not homologous to the primitive mouth, 
we can only refer him to the memoirs of Miiller, paisa and 
Le eggs for proof to the ¢ 
ag There seems no doubt, as Heckel insists, that . the majority 
to those which the sad categories of our systems have to 
one another. This change has pri incipally been brought about by 
a better knowledge of the embryology of a few well known types. 
“ But what Cag pune of all the Seon of Heckel which form 
the basis of his Gastrea theory? They are totally unsupported, 
and with their 60 must fall his theory; it can only take its 
place by the side of other physiophilosophical systems; they are in- 
genious arrangements laboriously built up in the interests of 
special theories, which fall to che ground the moment we test them 
by our actual knowledge. That the time has not yet come for 
maed hetgceag classifications, the attempts of Heckel plainly show, 
are in no ways in advance of the other embryological 
classifications which have preceded them; we get new names for 
somewhat differ 
- aeciestion based upon the value of embryonic la yers is at 
ovell oF disprov ed on the m 
