150 BAILEY AND TIPPER. 



"partial" larvae, derived from isolated blastomeres or egg fragments, 

 and in "double" larvae, from fused eggs, body size is directly pro- 

 portional to the number of constituent cells. As a result of these 

 observations upon echinids, he concludes (1900, p. 384) that, "die 

 Zellengrosse der zellen einzelner specifischer Organe scheint eine so 

 fest fixirte Grosse zu sein, wie es die optischen Richtungen am Krystall 

 sind." Schnegg (1902), in studying the genus Gunnera, records a 

 number of measurements which corroborate the work of Amelung. 

 Boveri (1904) shows that the epithelial cells, from tongues of dwarfs 

 and giants of the human species, are of the same size as those from 

 individuals of normal stature, and Schultz (1904) states (p. 559): 

 ^' so w^ill ich f iir die Planarien wenigstens das Gesetz aufstellen, dass 

 bei Verkleinerung der Form infolge von Inanition die Zellen nicht 

 an Grosse, sondern nur an Zahl abnehmen — und zwar in alien Or- 

 ganen Proportional den Grossen verhaltnissen dieser Organe zueinan- 

 der." Ewart (1906) concludes that, in unusually large leaves, formed 

 upon defoliated trees, there is an increase in the number, but not the 

 size of the cells. ^ 



Very different results are secured, however, by another group of 

 investigators. From his study of the spinal cord of the frog, Gaule 

 (1889) is led to place much emphasis upon the constancy of cell num- 

 ber. Donaldson (1895) similarly concludes (p. 162) that "the de- 

 termination of the number of neuroblasts occurs so early in the history 

 of the individual, and under such uniform conditions, that it is very 

 difficult to regard the en\ironment as possessed of much power to 

 cause variation in this respect." He considers that differences in the 

 weight of the human brain are due mainly to differences in the size 

 of the nerve cells. Hardesty (1902), who made a comparative study 

 of the spinal cords of various mammals, finds that the motor nerve 

 cells are largest in the elephant and smallest in the mouse. 



In view of the importance attached to the " Kernplasmarela- 

 tion" by Gerassimow (1902), Boveri (1905), Hertwig (1903) and others, 

 Gates' (1909) observations upon cell size in Oenothera (/ig(t,'<, a tetra- 

 ploid mutation of Oc. Lamarkiana, are of considerable interest. He 

 states (p. 543) : " In 0. gigns we have an organism built of bricks which 

 are larger and whose relative dimensions are also altered in some cases. 

 These two factors will apparently account for all the ditferences be- 

 tween 0. gigas and 0. Lamarkiana, and the second factor may be one 



2 More recently, Tenopyr (1918) endeavors to prove that differences in the 

 shaixj of leaves are ck'pcndent upon variations in the number rather than the 

 shape of their constituent ceils. 



