344 



SCIENCE 



[N. S. Vol. XXXII. Xo. 819 



discussed, representing- two hundred and 

 eighty-eight genera and fifty-five families. 



Students of Canadian birds are fortunate 

 in the possession of this cyclopedia of com- 

 prehensive and accurate information. It is 

 scarcely less interesting and valuable to the 

 ornithologists of the United States, who will 

 find in it a larger mass and greater detail of 

 reliable matter concerning many of our 

 species than is to be found in any other like 

 publication. It is a methodical, careful record 

 of data of observation, simply and clearly 

 written, for the compilation of which the au- 

 thors deserve the gratitude of all students of 

 American ornithology. 



Stephen A. Forbes 



Weitere experimentelle Untersuchungen uher 

 Artverdnderung, speziel uber das Wesen 

 quantitativer Artuntershiede hei Daph- 

 niden. By E. Woltereck, Vehr. der 

 Deutschen Zool. Gesellsch. 1909. Pp. 

 110-172, 18 text figures. 

 Dr. Woltereck has selected the very variable 

 longispina group of Daphnias for his studies 

 in variation and heredity and the results on 

 which the paper is based were obtained in ex- 

 periments covering a period of three years. 

 The plan of the investigation embraces a 

 study of four problems: (1) The cause, ex- 

 tent and character of the variations in this 

 group of crustaceans; (2) the characters pos- 

 sessed by hybrids resulting from the crossing, 

 of two elementary species; (3) whether a 

 pure culture biotype can be changed through 

 the selection of extreme variants; (4) whether 

 and how much a long-continued exposure to 

 a particular environmental condition will 

 change the characteristics of a biotype hered- 

 itarily. 



So far the experiments have been confined 

 mainly to the first problem and attention has 

 been directed chiefly to two characters, the 

 length of the helmet and sexuality. The au- 

 thor found that the length of the helmet is 

 dependent primarily on the quantity of food 

 (an external factor) and the number of the 

 generation (an internal factor). Indirectly 

 also it is affected by the temperature of the 

 water through its influence on assimilation 



and body activities. The length is directly 

 proportional to food assimilation and is not 

 affected directly by other external factors 

 such as salt or gas content of the water, light 

 or temperature. With respect to the internal 

 factor, the first generations produced by 

 ephippial eggs have small helmets but, under 

 the same food conditions, later generations 

 will have larger helmets. This seems to show 

 the presence of a " Helmhohepotenz " which 

 has become hereditarily fixed so that the size 

 of the helmet may be modified by food con- 

 ditions, but it can not be entirely controlled 

 by this factor. No mutations were observed. 



Concerning sexuality, it was found that the 

 sexual stage might be postponed for several 

 generations (ten to twelve) but it was not 

 possible to postpone this stage indefinitely in 

 all individuals. In some cases it became ob- 

 ligatory in aU individuals, while in other in- 

 stances it became only partial and facultative. 

 The parthenogenetic stage was found to be 

 obligatory in all generations. 



Dr. Woltereck also studied two regressive 

 characters, the pigment fleck (Nebenauge) 

 and the dorsal shell teeth. Some individuals, 

 especially those belonging to the earlier gen- 

 erations, possessed a rather large pigment 

 fleck while this character was entirely absent 

 in individuals belonging to later generations. 

 At first this was supposed to he a mutation 

 but further study revealed the presence of a 

 number of intermediate stages, thus showing 

 a continuous variation. Environment did 

 not seem to affect the variability of this char- 

 acter. 



The dorsal teeth also showed a continuous 

 variation in size, in position, and in herita- 

 bility. Through selection the number of in- 

 dividuals possessing these teeth was raised to 

 60 per cent, in the third generation. This 

 character was affected by a marked change 

 in the temperature of the water. If a female 

 having ripe eggs in her ovary were suddenly 

 transferred from water having a temperature 

 of 25° to water at 12° and kept at this tem- 

 perature, the young produced by these eggs 

 possessed dorsal teeth. 



One series of experiments is concerned with 



