QUEKETT MICROSCOPICAL CLUB, 251 



the circulation of the blood, and Hooke figured a section of cork 

 " divided into little boxes or cells." In 1677 Leeuwenhoek 

 discovered spermatozoa, but it was not till 1827 that Baer first 

 saw the mammalian ovum. In 1801 Bichat showed the body of 

 one of the higher animals to be a collection not only of organs, 

 but of tissues, and cellular structure was announced by Schleiden 

 and Schwann in 1839. In 1870-5 we knew only the nucleus and 

 nucleolus, and the lecturer remembered Dallinger demonstrating 

 the chromatin threads of the nucleus in 1886, All this was very 

 wonderful, but it only pushed the mystery farther back. Dr. 

 Leeson then went on to explain the miracle of miracles : how that 

 we all spring from the union of two cells through which are trans- 

 mitted the form and characteristics of our parents. In 1880 

 Weismann discovered that the germ-plasm is differentiated from 

 the body-plasm at a very early stage of development. The germ 

 cells, if they get a chance of suitable union, never decay. They 

 are like one-celled animals, which, unlike multicellular animals, 

 never really die. The individual is merely the guardian of the 

 race, the casket in which the reproductive cells are protected and 

 matured. The immortal germ-plasm is the source of the life 

 stream. The lecturer then described the differentiation of the 

 germ-plasm into male and female elements and the necessity for 

 the extrusion of the polar bodies from the ovum before union with 

 a sperm cell can take place. Surface tension may be a factor in 

 determining the contents of the polar bodies, but it is a matter 

 about which we know little. We resemble our ancestors because 

 we spring from the same germ-plasm, but we cannot tell what 

 characteristics we lose through the polar bodies. Bateson 

 thinks that evolution may be largely a question of loss and 

 favourable unpacking. The fertilised ovum divides into thou- 

 sands of cells which soon differentiate, and the fate of children 

 and grandchildren is settled by the separation of certain cells which 

 form the reproductive tissues. These are the most important 

 part of the creature, and the other cells serve them. Environment 

 does not alter the structure of the germ cells. It may and does 

 cause variation in unicellular animals in which there is no segre- 

 gation of the germ cells ; but as no rearrangement of the already 

 constructed germ-plasm is possible, so no personally acquired 

 characteristics are inherited. The chromosomes are the essential 

 part of the cell, and so chromatin is the physical basis of life. 



