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 of a 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 Histogenesis 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. 



