VI.] THE FRESH-WATER POLYPES. 347 



action of reagents, appears as a structureless membrane. 

 This furnishes attachment for the cells themselves and sup- 

 port for the body generally; its optical characters in the 

 prepared state are expressed in the term supporting lamella, 

 its real nature more nearly in that of mesoglcea. 



It is possible that the longitudinal fibres connected with 

 the cells of the ectoderm may be specially contractile, and 

 represent muscles; but, however this may be, each cell has 

 its own independent contractility. Similar fibres, disposed 

 transversely, arise from the bases of the endoderm cells. 

 These have been met with only in the body, and they ap- 

 pear to be in connection with the fibres of the ectoderm 

 cells, by means of delicate fibrils which perforate the above- 

 named mesoglcea. • 



LABORATORY WORK. 



1. Put into a beaker some water containing bodies to 

 which Hydrae are attached, and place the beaker in a 

 window not exposed to direct sunlight : in the course of 

 some hours many Hydrae will be found attached to that 

 side of the glass which is turned towards the light. Note 

 their size, form, colour, mode of attachment and move- 

 ments. 



2. Transfer a Hydra, by means of a pipette, on to a 

 slide with plenty of water. In order to avoid crushing, 

 place the animal between two coverslips, so arranged as 

 to support the edges of a third one which shall overlie it. 

 Examine with a low power. 



