The Natural History of Flatworms. 9 



a green scum on the surface of the sand when the tide had receded. 

 Experience had taught that creature that if it remained at the 

 surface of the sand when the incoming and receding tide passed 

 over the locality it would be mercilessly washed away and perish. 

 Thus while water covered the sand they retreated below the 

 surface to safety, and when the sea had retreated beyond their 

 habitation they rose to the surface once again. Past experience 

 had so affected the habits of convoluta that if individuals were 

 brought into the aquarium at every low-water period outside they 

 rose to the surface and sank below when the outside tide was in, 

 in spite of the fact that the tide stimulus was entirely removed. 

 In fact, they provided one with a perfectly accurate time-table. 

 Dealing with the subject of regeneration, the lecturer said 

 planarians reproduced their kind, exactly as did other animals, by 

 means of the fertilized egg. However, they might adopt another 

 method, common enough, it was true, known as spontaneous 

 division. It might occur by accident or by the deliberate action 

 of the animal itself, but, whatever the cause, the animal merely 

 became cleft in two, and each part builded up the missing portion, 

 two perfect animals resulting. 



STRUCTURE AND LIFE HISTORY OF LICHENS." 



By Mr. G. Livens, B.Sc. 



{Abstract) 



The Lecturkr in the course of his paper, said the answer to 

 the question. What is a lichen ? seemed a simple one to answer, 

 but it was usually the simple one that was most difficult to answer. 

 Should one ask what is a rose — he meant a rose in the widest 

 sense— one had to consider all the members of the rose tribe to 

 find characters or combinations of characters shared by every 

 member, and which were not shared by other plants. Such 



