ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 165 



on the other hand, is a recessive character. Its appearance is always 

 prevented, either by the maternal or by the paternal influence. 



Echinoid Hybrids.* — Cresswell Shearer, Walter De Morgan, and 

 H.M. Fuchs previously found that the late larval characters of Echinoid 

 hybrid larvEe were invariably maternal — that is to say, that the late 

 larval hybrid always resembled its mother. A continuation of the ex- 

 periments has shown that in late larval life some of the hybrid crosses 

 are as markedly paternal as they were previously maternal. The com- 

 plete change in heredity from one year to another is very striking. It 

 seems most probable that some factor in the environment has affected 

 the metabolism of Echinus miliaris (the maternal species used) in its 

 habitat, so that the condition of the female germ-cells has changed. 



Effects of Hypertonic Solutions on Fertilized Ova. t — J. Grray 

 finds that in hypertonic solutions the chromatin of Echinus acutus 

 behaves differently from that of E. esculentus. The effect of hypertonic 

 solutions of a certain strength on the fertilized eggs of E. acutus is to 

 cause the elimination of chromosomes from the nuclei by a process 

 exactly similar to that which is normally found in the hybrid eggs of the 

 cross E. esculentus <S x E. acutus ? . This phenomenon cannot be in- 

 duced in the fertilized eo'SfS of E. esculentus bv similar treatment. 



In eggs of which the whole nuclear structure has been disorganized, 

 the first segmentation- division is normal. The later segmentation of all 

 eggs which have been treated with hypertonic solutions is abnormal. 



It is possible that the hypertonic solutions exert a tonic action upon 

 the nucleus, by upsetting the normal relationship of the cytoplasm to 

 electrolytic ions. The permeability of the egg is changed when a 

 spermatozoon enters, and presumably the change is constant in degree 

 for each species. AYhen, however, the sperm of a foreign species is 

 made to enter the egg, it may be that the change of permeability is not 

 that which would occur after the entrance of a sperm of the species to 

 which the egg belongs. 



Early Stag-es of Segmentation in Echinus Hybrids. J — L. Doncaster 

 and J. Gray have studied in particular the question of the elimination 

 of chromosomes in crosses of Echinus miliaris and E. esculentus or 

 E. acutus. They find that E. esculentus 9 x E. miliaris i behaves 

 normally, with no ehmination, while E. miliaris 9 x E. esculentus or 

 E. acutus shows only a small percentage of developing eggs, of which 

 a considerable portion at least show elimination of one, or at most a few 

 chromosomes. 



The experiments give evidence of a physiological differentiation 

 among the chromosomes. Some behave normally, others form vesicles, 

 or fail to divide. The hypothesis is discussed whether the vesicle- 

 formation depends on the disturbance of the osmotic relations between 

 the chromosomes and the cytoplasm. 



* Quart. Journ. Micr. Sci., Iviii. (1912) pp. 337-52 (2 pis. and 4 figs.). 

 t Quart. Journ. Micr. Sci., Iviii. (1913) pp. 447-81 (4 pis. and 4 figs.). 

 I Quart. Journ. Mier. Sci., Iviii. (1913) pp. 483-510 (2 pis.). 



