Miscellaneous. 89 



his subsequent generalizations of the value for systematic purposes 

 of these two layers ? The distiuction 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 I'lanido' 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 embrj'onie 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 fonued of the entodenii ; 

 and when Hackel states the result (the Gm^tnda) to be the same 

 whether formed by the ectoderm or entoderm, he states what is known 

 to be exactly the contrary. It is not known, as is stated by Hiickel, 

 that the mere fact of a Planula fixing itself by one extremity or not, 

 will in one ease lead to a radical t}ije, in another to a bilateral 

 type. AMiat becomes of all the free-swimming embryos of Echi- 

 noderms, of Acalephs, of Polyps ? Are they bilateral ? It is true 

 Hiickel 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. 

 ^^'hen he says that Sars, whose knowledge of the development of 

 Echinoderms was so accurate, agreed with his peciiliar views, we 

 can only reply that his agreement must be based upon a misunder- 

 standing. ^^'e have equally as many radial and bilateral types 

 developed either from fixed or from pelagic Gastndce ; and to cite 

 this as a causa efficiens, the mechanical reason of the genetic descent 

 of all radiates from a fixed Gastnda, and of all bilateral types from 

 a free-swimming one, is simply fantastic. How is it that so many 

 Actiniae 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 Gastnda of 

 other Yertebrates than Amj)liioxvs it is idle to talk of the continuity 

 existing between the ontogeny of Amphioxus 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 Oastrula 

 form ! Neither Hiickel nor any one else has seen this ; it is a 

 prettA' hint which may or may not be proved. 



Considerable confusion arises in Hiiekel's classification from his 

 adopting at one time as of primary importance the develojjment of 

 the cavity of the body and making it the main point in his ])hylo- 

 genetic classification, while previously the relations of the phylum to 

 Protasnts and ProtJiehnis (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 



