414 DR. A. FARRE ON THE STRUCTURE OF THE CILIOBRACHIATE POLYPI. 
in vei-y regular order, the smaller cells as in Membranipora, growing from the upper 
and inner sides of the larger ones immediately below them. 
It is evident that in the construction of the cell, Membranipora and Notamia are 
closely allied, and notwithstanding the encrusting character of the former species, 
and the ramified habit of the latter, it would be easy in imagination to convert the 
one into the other by supposing two lines of growing cells, such as are often seen in 
M. pilosa, to be attached back to back to each other : from these similar branches 
arising the encrusting species would be converted into the ramifying one. And the 
further passage of this to the arrangement in Flustra is accomplished simply by the 
union of a parallel series of such branches. 
Such then are the principal facts that have offered themselves to my notice during 
the investigation of the above described species. They afford evidence of the ex- 
istence of a very decided type of structure, and one which presents a remarkable 
uniformity of character, notwithstanding that it was observed in genera differing con- 
siderably in less important particulars. To what extent, however, this prevails, and 
how far it may be modified in other genera, are considerations which must be re- 
served for a more extended inquiry to determine. Among the points requiring 
further elucidation, one of the most important is the condition of the nervous system. 
No trace of either nerves or ganglia could be detected ; yet the attributes of a nervous 
system were so clearly exhibited as to leave no doubt but that this must exist, and 
probably in some degree of perfection. Not only was the delicacy of their sense of 
touch very strongly marked, but the operations also consequent upon the enjoyment 
of such a sense were sometimes singularly striking. This is seen in the instant re- 
tiring of the animal on the slightest alarm, and the caution which it sometimes shows 
before emerging again from its cell* ; in the obvious selection of its food ; and in the 
pertinacity with which it refuses to expose itself to water that has become in the least 
degree deteriorated. 
The respiratory system, again, being so intimately connected with the digestive 
apparatus, it becomes difficult to determine, from witnessing the combined operations 
of the parts, in what degree they contribute to the performance of each function re- 
spectively. The peculiar action by which the pharynx becomes so frequently dis- 
tended, and the constancy of the currents produced by the tentacular cilia, (appa- 
rently far beyond what would be necessary to afford a sufficient supply of food,) 
* On several occasions I observed in Halodactylus one or more of the tentacles protruded and turned over 
the side of the cell before the animal ventured out again, after having been alarmed by the sudden contact of 
some vibriones that abounded in the water used, as if to ascertain the presence or absence of the intruder (plate 
xxvi. f. 7. b.) ; a position of the arms which is also frequently assumed in this species in the act of retiring. 
So delicate indeed is the sense of touch, that the creeping of a very small animalcule over the top of one of the 
closed cells was followed instantly by a shrinking of the soft parts beneath. 
