154 JoiRNAL OF TIIK ^flTCHKLL SoCIKTY ID 



ec. 



It has also boon sliown that tlie chromatin of a penetrat- 

 ing sperm may be eliminated from the developmental pro- 

 cesses. Both Boveri and Teiohmann have fertilized egps of 

 Echinns with sperm treated with potash solution, and though 

 the sperm entered the eug and intiated development, the 

 sperm nnclens did not fuse with the egg nuclens. Loeb and 

 later Knpelwieser caused sea-urchin eggs to develop by adding 

 sperm of ]\rytilus (a salt water mussel). The sperm entered 

 the egg but the head of the sperm with its chromatin took 

 no true jiart in the development. 



Since first putting fortli his thcoi'v that it is the cliT'oma- 

 tin that is chicHy injured by treatment with radium, the 

 evidence in favoi- of it has been added To by fni'ther experi- 

 ments by Ilertwig, by his son Gunther llcrtwig. and by 

 Opperman. Oskar llertwig has f(mnd in the larvae of Triton 

 obtained from sound eggs fertilized with ii'i'adiated sperm, 

 that the nuclei of the body cells have only half or the re- 

 duced number of chromosomes, the male chromosome com- 

 plex having failed to take its part in development. Gunther 

 HerTwig has shown that by intensive radiation of several 

 hours duration sperm threads of the sea-urchin arc so af- 

 fected that though they are able to penetrate the es^g and 

 stimulate development, they lose their ability to form normal 

 chromosomes and thus are elimimited from development. He 

 also found that in frog eggs treated with radium and fer- 

 tilized with normal sperm, the injury increas?s with the 

 duration of the radiation up to a maxinmm and from there on 

 decreases again as the radiation is prolonged — as his father 

 found for sound eggs fertilized wits radiated sperm. Only 

 the radiated nuclei show the effects of the treatment. In 

 the frog then development is possible with only a haploid 

 nucleus, i. e.. only the half of the nucleus derived from one 

 of the parents. Where the injury is severe to either the ep;g: 

 or the sperm nucleus, the other is able to carry on the de- 

 velopment, and in tact there is less deviation from the 

 normal course of development than in the case where both 

 nuclei are injured only slightly. All of this evidence seems 



