ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
637 
his studies of the internal anatomy of Echinoids Mr. Bury chiefly made 
use of Echinus microtuberculatus. After some account of the Ophiurids 
and Crinoids the author passes to the second part of his essay which 
deals with phylogeny. The hypotheses of preceding authors are 
critically discussed, and an attack is made on the almost universal 
method of deriving all existing forms from the Cystidea. The author 
thinks that if palaeontologists have really proved beyond any reasonable 
doubt that the Echinozoa are derived from fixed forms, then ontogeny is 
misleading, but it is doubtful whether palaeontologists have so completely 
established their position as to compel us to accept it. Without pursuing 
the subject further Mr. Bury submits that until palaeontologists have 
produced some far more striking intermediate forms between fixed 
Cystids and free Echinozoa than are at present forthcoming, embryo- 
logists may be forgiven if they do not follow them. Dealing next with 
the bilateral ancestor, and passing on to consider the transition to radial 
symmetry, it is suggested that the generative organs appear to have 
followed the new, that is radial, symmetry at a very early period. 
Whether the skeleton was or was not one of the first structures to 
assume radial symmetry, is a question which is still too much under 
discussion for Mr. Bury to attempt to decide it. With regard to the 
origin of the Pelmatozoa Mr. Bury points out that he has good reasons 
for believing that the Echinozoa were never fixed by the aboral pole, 
and that the utmost that embryological evidence will allow of is a 
fixation of the bilateral ancestor by the prgeoral lobe. The existence of 
a sucker is certainly possible, though the evidence for it is weak, and 
the assumption of it does not appear to be necessary. It becomes there- 
fore worth while to consider whether the supposition that the Pelmatozoa 
become fixed after the change of symmetry, instead of before it, is not 
at least as probable. Although the suggestions as to the origin of the 
Pelmatozoa which Mr. Bury makes are, he allows, of an extremely 
speculative character, and will require a great deal of evidence to support 
them, yet a too rigid adherence to the apparent teachings of the larva of 
Antedon is equally objectionable. It may be urged that at present we 
only know the development of one Pelmatozoan larva, and we have no 
reason for regarding this as especially primitive ; on the contrary, the 
very early loss of bilateral symmetry in the arrangement of the body 
cavities, as well as the entire absence, before fixation, of either 
oesophagus or intestine, point most conclusively to it being a much 
altered form. With regard to the origin of Holothurians, the facts 
within our knowledge are as yet insufficient to allow us to do more than 
offer some cautious suggestions. Mr. Bury is inclined to the belief 
that this class separated off very early, perhaps even before the Pelma- 
tozoa. 
Lastly the relation of the Echinoderma to the Enteropneusta is 
considered, and the author claims to have established a case in favour 
of the homology of the dorsal sac and dorsal organ of the former with 
the pericardium and proboscis gland of the latter, which cannot be 
lightly set aside. Taking this in connection with other resemblances 
between the two groups we seem to have a chain of evidence of their 
connection which is at least as strong as that which binds together any 
two of the great subdivisions of the Animal Kingdom. 
