524 
circular canal probably originates in lateral branches from the distal 
extremity of the deep gastro-vascular canal ; but the author failed 
in satisfactorily tracing its mode of development. Four out of the 
eight superficial gastro-vascular or ctenophoral canals, namely those 
which corresponded to the narrow sides of the digestive cavity, had 
also opened into the circular canal ; but the other four meridional 
canals, though extending for some distance beyond the oral extre- 
mities of the meridional bands, had not yet opened into it, and 
terminated towards the mouth, each in a blind extremity. The 
eight meridional canals had begun to send out their csecal offsets ; 
but these were as yet few in number, and simple. Individuals of 
about three-fourths of an inch in length had all the gastro-vascular 
canals in communication with the circular canal. The caeca had 
become numerous and ramified, and the capillary tubes appeared 
fully developed. The meridional bands, however, had not yet 
attained their full extent, their oral termination being still separated 
from the mouth by a distance equal to about one-third of the entire 
meridional length of the animal ; while the generative organs had 
not yet made their appearance, and the processes of the tentacular 
discs were nearly simple. 
3. On the Anatomy and Classification of the Heteropoda, By 
John Denis Macdonald, Esq., R.N., F.R.S., Surgeon of 
H. M.S. “ Icarus.’’ Communicated by Dr Douglas Mac- 
lagan. 
The author considers the usual division of the Heteropoda into 
the two families of Firolidae, and Atlantidse as unsatisfactory, and 
arranges them in three families, according to the following zoologi- 
cal characters. 
HETEROPODA. 
I. Gymnosomata ( Firolidce ). Animal wholly naked or without a 
shell. 
I. With slender tentacula,and destitute of true branchiae. Visceral 
mass near the root of the filiform process of the Meta- 
podium — - Firoloides . 
2. With rudimentary or no tentacula, but furnished with true 
branchiae. Visceral mass considerably in advance of the base 
of the filiform process of the Metapodium — Firola. 
