202 



THE MICROSCOPE. 



weather the polyp shall continue its propagation not by budding, but 

 by eggs ; the latter being better calculated to protect the tender thread 

 of life within against the destructive frosts of winter, than could pos- 

 sibly be resisted by the delicate construction of a new-born fragile 

 creature thrust into its nipping influence. 



There are other British kinds : the Hydra verrucosa, which is of a pale 

 ashy colour, with six moderately long arras ; and the Hydra lutea, a 

 marine species, with a large head and ten very short arms. 



Every reflecting person who reads even the slight sketch we have 

 given of this polyp tribe must be struck with astonishment at a creature 

 so primitive in structure, possessing the actions, sensations, and powers 

 of higher organised beings. The stomach is but one simple structure- 

 less membrane, or cell, the external surface-cells condensed so as to 

 form a kind of double skin ; and the inside a mere wall of cells running 

 crosswise, possessed of a velvet- like surface, the substance being red or 

 brown grains held together by a sort of gluey substance. 



This singular formation for the functions of animal life has led to 

 many learned surmises and discussions tending to the most important 

 results in the science of physiology. 



SERTULARIDJ3. 



The second family of polyps are the interesting and beautiful Ser- 

 tularidce ; they are readily attainable on our own sea-shores. Linnaeus 

 made a large genus of them ; but Lamarck considerably reduced his 

 classification. The usual type presented is the beautiful Sertularia 



pluma, fig. 105, which Dr. Fleming pro- 

 poses to divide into two groups, accord- 

 ing as the stems are simple or compound. 

 The Sertularia have arms or feelers, 

 which are abundantly supplied with cilia, 

 with pitcher-shaped, dwarfish cells, ar- 

 ranged alternately, or in pairs obliquely, 

 not exactly opposite, on the stem and 

 branches of the polypidom, which is 

 horny, fistulous generally, but attached 

 in zigzag radiant fibres. 



Within this family come the Thoa, 

 of Lamouroux, of which there have been 

 several kinds found in Great Britain. 



fig. 105. A single branch of Ser- 

 tularia. 



The name is supposed to be derived from 



