ADAPTATION AND INHERITANCE KAMMEEER. 425 



Another Polychsete fresh-water worm (Lumbriculus, fig. 3), possesses 

 like the rest of the worms, the ability to develop into new worms, 

 from pieces cut from the body. However, according to Morgulis, 

 not all parts of the body are able to accomplish this. If five segments 

 are taken from the anterior region of the body (A), these will yield 

 exactly double as many caudal segments as five segments taken from 

 the posterior portion (J5) are able to yield. After 14 days the new 

 tails, a, J), are detached and these now produce a new head anter- 

 iorly; a^, &i, so that complete worms, although they are somewhat 

 dwarfed, are again produced. These dwarfed worms are again 

 robbed of their tails and must sprout another last set of tails. But 

 one of these forms {B), produces only about half as many tail seg- 

 ments as the other {A). This is the result of the stronger growth 

 power of the anterior end of the origmal worm, while the other is the 

 result of the lesser growth power of the posterior segments of the 

 original worm. The peculiar abilities of these parts have been 

 retained in spite of the fact that the pieces were finally subjected to 

 the same process — that is, to produce caudal segments of the head 

 end. Differently stated, the anterior end, derived from the posterior 

 end, has acquired the character of lesser development and transmits 

 this to its progeny even asexually. 



Recently the question of acquired characters has been diligently 

 studied in small crustaceans. Their reproduction is a sexual one, 

 in so far as it does not take place through budding or fission, but 

 through the production of true germ cells. But it does not agree 

 with our idea of orthodox sexual reproduction, since many genera- 

 tions may pass without the appearance of males. The reproductive 

 products at such times are purely feminme — that is, eggs which 

 develop without having been fertilized by a male cell, the sperma- 

 tozoan. We may distinguish this form of reproduction from sexual 

 reproduction, in the restricted sense, or bisexual reproduction, as 

 unisexual or parthenogenetic rej)ro(]uction. The investigators who 

 have been engaged in the study of these lower crustaceans, and have 

 in part or whoUy bred them parthenogenetically from unfertilized 

 eggs, have avoided the criticism which has often been expressed where 

 animals were produced by the bisexual method of reproduction, 

 namely, that the changes obtained in these animals, the ])roduct of 

 bisexual re])roduction, were not due to an adaptation to the environ- 

 ment, but to the crossing of races, in which certain characters, which 

 had up to this time been hidden in the gcrmplasm, had come to the 

 surface. To the breeding experiments, in which the above criticism 

 can not apply, belongs, among others of recent date, also one of the 

 most important older works, the experiments of Schmankcwitsch 

 (1875). This deals with the effect produced upon the form of the 

 saline crustacean {Artemia salina, fig. 4, 1), by varying the salinity 



