FKOGS AND TADPOLES. 2G9 



commenced, was very different from that we enjoy at the pre- 

 sent time ; and, in fact, that condition would have precluded all 

 possibility of the existence of Life as we find it to-day. "We 

 must assume that the earliest forms of life were unicellular, and 

 that a gradual development has taken place from this humble 

 beginning; and as the earth gradually changed and became more 

 favourable to life, so higher organisms would be able to subsist. 

 The first variation from the primitive type would be the 

 llastula, or, a colony of equal and similar cells; and then the 

 gastrula, when a division of labour sets in, — certain cells being 

 protective, others nutritive — and as each stage in progression is 

 reached it would be the starting point for innumerable new de- 

 velopments. Some of these might attain further advancement ; 

 while others, perhaps failing to make the most of their oppor- 

 tunities, or the force of circumstances, rendering further progres- 

 sion impossible, their higher development is limited, and they 

 either remain stationary or drop out of existence. They are 

 merely branches from the main trunk, from the summit of which 

 only continuous growth and development is possible. 



The Lecture was illustrated by a series of lantern slides show- 

 ing the stages in the development of the Frog, together with 

 various persistent unicellular, blastula, gastrula, and perenni- 

 branchiate forms, and the changes in the circulation from the 

 Tadpole to the Frog, concluding with illustrations of various 

 kinds of allied forms — Edible frog — Flying frog — Flying dragon 

 —Surinam toad, etc. 



Leciuee, No. 3. — The Structure of Timber. By Prof. Wiiiiam 

 SoMEEViLLE, Ph.D., B.Sc, F.L.S., etc., Feb. 25th, 1893. 



When asked to contribute a lecture to the present course, I 

 thought it might not be uninteresting if I endeavoured to give a 

 general sketch of the structure and mode of formation of an 

 economic product that ministers greatly to our comfort and neces- 

 sities. My object, however, is not to enter much into the minute 



