CILIATION OF ECTODERM OF AMPHIBIAN EMBRYO. 479 
regarded as homologous with the longitudinal ciliated band of 
Auricularia, it is the ectodermal space between the bands of the 
latter which may be regarded as the homologue of the neural 
plate of Vertebrata, and the longitudinal ciliated bands would 
perhaps be more exactly represented in the craniate embryo 
by the system of branchial sense-organs. ‘The possibility of a 
connection between the Chordate and Echinoderm phyla has 
been very often suggested; and in view of the remarkable 
agreement of the actual ontogenetic fate of the blastopore in 
both these groups the idea of a possible relationship between 
the phyla would be much more favorably considered were it 
not for the very general belief in the concrescence theory of 
vertebrate development. It is only by some form of concres- 
cence in development that it is in any way possible to bring 
embryological evidence in favour of the theory of vertebrate 
descent from a gastrula with an elongated mouth, one end of 
which gave rise to the present vertebrate mouth, the other the 
vertebrate anus. 
It should of course be remembered that cilia are of very 
general occurrence in the animal kingdom, that they are found 
in the simplest as well as the most highly differentiated types, 
and that they appear at the later as well as the earliest stages 
of development. 
These facts lead one to suppose that cilia may be with great 
ease acquired by an organism. The ciliation of the Amphibian 
may be only an ontogenetic adaptation. If the ciliation of the 
tadpole is a purely coenogenetic feature, what purpose does it 
subserve ? 
There can be very little doubt that, on the whole, it is re- 
spiratory. As regards the three special systems described in 
this paper, one, that connected with the cement-gland, has a 
very obvious use, and may very probably be a recent modifica- 
tion of a general ciliation of the ectoderm. 
The second, that connected with nasal epithelium and gill- 
filaments, has also a very obvious use in producing a very rapid 
flow over the gill-filaments, and very possibly its connection 
with the olfactory epithelium may be advantageous. 
