THE DISCOVERER 77 



that the composition of the blood of the lancelet, a 

 very low vertebrate, approached that of the blood of 

 the higher vertebrates, we find his work on the Me- 

 dusae followed by a further contribution to knowledge 

 of organic relation in an examination of the structure 

 of the sea-squirts, or Ascidians, so called from their 

 resemblance to a double-necked bottle (Greek askidion, 

 a small bottle). These animals are found singly, and 

 also in clusters, and interest in them, as hinted in the 

 quotation from Professor Allman, has deepened since 

 the discovery that they are in the line of the develop- 

 ment from invertebrate to vertebrate which ends in 

 man himself. Still feeling his way towards the great 

 central doctrine of unity, denial of which is the only 

 heresy from which a man need pray to be delivered, 

 Huxley made Schwann's cell-theory the basis of ex- 

 amination into the identity of structure in plants and 

 animals. He showed — and this with luminous skill 

 in the famous " lay sermon " on " The Physical Basis 

 of Life " — that the cell is the unit of structure, and 

 not the unit of function ; that, in technical terms, it 

 is morphological, not physiological, the u protoplasm " 

 being the fundamental element. "Although," re- 

 marks Professor Ray Lankester — 



it is forty years since the " Review of the Cell 

 Theory" was published, and although our knowledge 

 of cell-structure has made immense progress during 



