TADPOLES AND FROGS 213 



frogs at Baden, near Vienna, in order to observe (in the 

 laboratory of the celebrated microscopist, Professor 

 Strieker, the most gifted of his day) the earliest changes in 

 the little black egg, the size of a rape-seed, which follow 

 upon fertilisation. Properly placed in a watch-glass full 

 of water under a low power of the microscope one little 

 egg could be watched for hours. If it had not been 

 fertilised, nothing occurred. But if it had been, then 

 there were strange movements of its surface and a 

 puckering and sinking in along one definite line, coming 

 and going, but at last becoming well marked like a deep 

 furrow. Without actually splitting, the little sphere was 

 divided by the cleft into two halves. Then, at right 

 angles to the first cleft, a second began to form, and so 

 on, until in the course of hours the sphere became divided 

 on its surface like a blackberry. The separate pieces 

 thus marked out are the first " cells," or units, of living 

 protoplasm of the young tadpole. They continue to 

 divide and to chemically convert the granular matter 

 with which they are charged into living material whilst 

 the mass slowly, in the course of days (taking up water 

 for its increase in actual size), becomes elongated, and 

 shows the rudiments of head, eyes, ears, spinal cord, and 

 projecting tail. It is a fascinating task to watch this 

 gradual development and a difficult, but necessary, one 

 (which has now been carried out in the minutest detail 

 by patient students), to harden with chemical solutions 

 the growing embryos taken at successive stages, to embed 

 them in wax or paraffin (as Strieker was the first to do), 

 and to cut them into the finest slices, then to clarify 

 these slices in balsam-varnish, examine them with the 

 microscope, and record and draw every "cell," every 

 constituent unit, as they increase in number and com- 

 plication of arrangement. That wonderfully difficult feat 

 has now been carried out not only in the case of the frog 



