445 
lined by a direct’ continuation of the endoderm of the body, 
and communicates by a distinct orifice with the stomach. 
Between the ectoderm and endoderm may occasionally be 
witnessed the appearance of longitudinal fibres, which would 
indicate the existence here of a true muscular apparatus. 
This, however, has not been made out so satisfactorily as to 
remove all doubts of its presence. 
The thread-cells of hydra are of two kinds, namely, the 
hastigerous and tactile organs of Corda. They are both de- 
veloped in the interior of cells, which, as secondary cells, 
originate free, and almost always solitary, in the interior of the 
ectodermal cells. The author’s examination of the structure 
of the hastigerous organs confirms the description given by 
Hancock.* The so-called tactile organs have not been cor- 
rectly described; each consists ofa capsule, having a filament 
coiled up spirally within it, and uncoiling in the act of pro- 
jection. 
The observations contained in the present communication 
were made on Hydra fusca. 
Dr. Lyons read the following notice of Researches on the 
primary stages of Histogenesis and Histolysis. 
Much yet remains to be achieved by chemical and micro- _ 
scopic researches, before we shall be in a position to understand 
thoroughly the laws, in obedience to which the elementary 
bodies combine to form organic compounds, and the processes 
by which these latter assume the determinate forms and dis- 
tinctive characters of the various vegetable and animal tissues. 
The term Hisrocenesis is employed to designate the 
origin, development, and growth of animal and vegetable tis- 
sues, and under this head are included several of the most 
‘obscure and difficult problems in the entire domain of physio- 
logical science. ‘Thus we have still to inquire what it is that 
determines the formation of plastic fluids; what are the forces 
* Annals Nat. Hist., 1850. 
