74 HUXLEY 



years, when Huxley's sense of humour would impel 

 him to remind Faraday of the lesson learned from 

 him. 



The more important of Huxley's original contribu- 

 tions to biological science may now be set forth, with 

 as much freedom from technical terms as the subjects 

 permit. 



The discoveries of Schleiden and Schwann in cell- 

 structure, as well as those of Von Baer in compara- 

 tive embryology, were known to Huxley when, 

 " with microscope lashed to the mast," he examined 

 the fragile organisms, « as the sand of the seashore 

 innumerable." To those discoveries he made an im- 

 portant addition in detecting that the Medusa are 

 built up of two cell-layers, or « foundation-mem- 

 branes," enclosing a stomach-cavity. From the outer 

 layer the skin and nervous system (as to the ex- 

 istence of which latter, since proven, Huxley was at 

 the time doubtful) are developed ; and from the inner 

 layer the alimentary and other organs are developed. 

 He also found that the reproductive organs are exter- 

 nal, and that all the Medusa have thread-cells where- 

 with poison is discharged at their prey. He then 

 made search for the presence of these several features 

 in other families of the Hydrozoa, and found unity 

 of plan throughout. In modern classification, there 

 are three grades of animals : the Protozoa, which em- 



