484 SUMMARY OF CURRENT RESEARCHES RELATING TO 



near a tube of radium. It seems as if the rays acted on the chromatin 

 of the nucleus, increasing its activity or after a while destroying it. 

 They destroy spermatozoa (practically naked chromatin), but excite the 

 protected chromatin of the ovum and determine parthenogenesis. They 

 induce on the chromatin of the fertilised ovum certain durable effects 

 which are as it were retained unexpressed until growth or renovation 

 sets in. There seems to be no effect on tissues except when they are in 

 process of growth or differentiation. 



Influence of Alcohol on Development.* — H. E. Ziegler has experi- 

 mented with the ova of the sea-urchins Echinus microtuberculatus and 

 Strong ylocentrotus Hindus to test the influence of alcohol on develop- 

 ment. The presence of ■ 5-1 p.c. does not result in serious injury, 

 normal Plutei may result, but there seem to be marked individual differ- 

 ences in susceptibility. The presence of 2 p.c. seriously disturbs 

 development, and seems to act as a poison, as Pauber also found.f The 

 cleavage is slow and often abnormal, only a few blastulse are formed, the 

 blastoccel tends to be too small, there are too many mesenchyme cells. 

 Gastrulation is sluggish, the mesenchyme cells have not their normal 

 arrangement, if a skeleton is formed at all it is abnormal, Plutei with 

 well-developed arms do not occur. "With 3 p.c. of alcohol in the sea- 

 water, few blastulse are formed, and there is no gastrulation. "With 

 4 p.c. no blastulas are developed. 



The general result is a disturbance of the cell-division ; it tends to be . 

 inhibited. Thus there may be nuclear division without cell-division. 

 Another noteworthy effect is an inhibition of cell-movements, e.g. in 

 gastrulation. Of especial interest is the formation of larvae without any 

 skeleton, — as it were a return to a more primitive larval type. 



(Estrous Cycle and Corpus Luteum in Sheep.}— F. H. A. Marshall 

 finds that in Scottish black-faced sheep the length of the sexual season 

 varies with the locality, both in regard to the number of dicestrous cycles 

 in a season and to the duration of each cycle. There is a perfect 

 gradation between the moncestrous condition of some wild sheep and the 

 extreme poly oestrum of certain merinos. 



The procestrum is marked by a mucous or sanguineo-mucous flow. 

 It is very rapidly succeeded by oestrus (the period of desire), the two 

 periods frequently seeming to occur simultaneously because of the 

 abbreviation of the process. 



The changes through which the sheep's uterus passes during a single 

 dicestrous cycle can be divided into four periods : — (1) period of rest ; 

 (2) period of growth and increase of vessels ; (3) period of breaking 

 down of vessels and extravasation of blood ; and (4) period of recupera- 

 tion and pigment formation. The homology between the dicestrous 

 cycle in the sheep and the menstrual cycle of the Primates is rendered 

 very probable. 



Ovulation can occur spontaneously at any oestrous (or pro-cestrous) 

 period with Scottish black-faced sheep, excepting at certain cestri outside 



* Biol. Centralbl., xxiii. (1903) pp. 448-55 (5 fi*s.). 



t ' WirkuDgen des Alcohols auf Tiere und Pflanzen,' Leipzig, 1902. 



X Proc. R. Soc. London, lxxi. (1903) pp. 354-5. 



