GENEOLOGICAL. 381 



acknowledged chief of monster-makers. He has ex- 

 perimented for instance, with the egg of the fowl, — 

 a corpus vile for many purposes — placing it verti- 

 cally instead of horizontally, keeping it slightly 

 above or slightly below the normal temperature of 

 incubation, heating different parts of the egg un- 

 equally, hermetically varnishing part of the shell, 

 and so on. He has not only shown that the germ 

 is plastic in the grip of its environment, but he has 

 been able to induce a number of particular malfor- 

 mations which are of interest to the student of 

 normal structure. 



Of great importance, perhaps inadequately recog- 

 nised, is the work of Prof. A. Rauber " Formbildung 

 und Formstorung "^ (1880), which showed the sig- 

 nificance of relating the results of abnormal disturb- 

 ance to the normal sequence of events, and described 

 a number of interesting experiments. To it we may 

 refer the serious student for a historical sketch of the 

 results achieved before 1880. 



There are many other workers, such as O. Hert- 

 wig, B. C. A. Windle, and Ch. Fere, whose investi- 

 gations are in part on the same lines as those of 

 Dareste and Rauber. 



(h) Puncturing Experiments. — The egg of the 

 frog, about one-tenth of an inch in diameter, is a very 

 convenient subject for embryological experiment. 

 The first three cleavages, visible even with the naked 

 eye, lie along three planes, Avhich, in order of se- 

 quence, correspond to those which divide the tadpole 

 into right and left sides, head and tail regions, dorsal 

 and ventral areas. Of the first two cells into which 

 the egg of a frog divides one has in it the material 

 for forming the right half of the body, the other has 

 * I.e., Forming and deforming. 



