32 MARINE BIOLOGICAL LABORATORY. 



what the bond of unity actually lies. He would have no 

 conception of what Huxley has called ''the physical 

 basis of life," and the structural unit of all organisms 

 would lie wholly beyond the range of his perception. 

 That isthmus of small life between the animal and vege- 

 table kingdoms, his unaided vision would never discover. 

 In searching for intermediate forms, he would inevitably 

 be led astray by those deceptive appearances under 

 which adaptive development and degeneration have con- 

 cealed so many ancestral relationships. Sessile animals, 

 like the sponges, the hydroid polyps, the sea-anemones, 

 the polyzoa or moss polyps, the ascidians, and many 

 others from the higher as well as the lower classes, 

 would be separated from animals having the power of 

 locomotion, and be regarded either as plants, or as forms 

 representing both plants and animals. Where immobil- 

 ity is combined with the branching form, as in the 

 hydroid polyps, the disguise would be complete. Even 

 Linne, the great lawgiver in systematic biology, de- 

 scribed such forms in the tenth edition of his " Systema 

 Naturae" as ''plants with animal flowers"; and in the 

 twelfth edition, which concluded his systematic work, 

 he held to the opinion that the stock of the hydroid col- 

 ony is a true plant, while its " flowers " are true animals. 

 This idea was embodied in the word zoophytes, plant- 

 animals, a word that has done varied service in system- 

 atic zoology from the middle of the i6th century. 



The utter insufficiency of external characters as a guide 

 to genetic affinity, is well seen when we come to such 

 forms as the so-called compound ascidians, which are 

 found encrusting the rocks along the shore. At first 

 sight one would not even detect any signs of life here, 



