SUMMARY OF CURRENT RESEARCHES. 11 



mean number of pigs per litter being 5 * 97, the mode 6. Of the 5790 pigs, 

 3024 were males and 2946 were females'; 102* 6+ males to 100 females. 

 In the whole population the nipples ranged from 8 to IK, with a mean 

 of 12*2 + and a mode of 12. In the male pigs the nipples ranged from 

 9 to 18, Avith a mean of 12 -4 + and a mode of 12, and a standard devi- 

 ation of 0*6906+ 0*0060. In the female pigs the range was from 

 8 to 18, with a mean of 11 • 9 + , a mode of 12, and a standard deviation 

 of 0-7905± 0-0069. 



On the left side the nipples ranged from 4 to 9, with a mean of 

 6 - 1 and a mode of 6 ; on the right side they ranged from 4 to 10, with 

 a mean of 6"1 — , and a mode of 6. The coefficient of correlation for 

 the two sides was 0-60631 0-0055. In the whole population the 

 arrangement of the nipples fell under the regular plan (one in which 

 the nipples are grouped in pairs right and left) in 3559 cases, and under 

 the irregular plan (one in which the members of the right and left series 

 show no obvious pairing) in 2411 cases. 



There is no obvious relation between the size of the litter and the 

 number of nipples in the females. Though there may be as few nipples 

 as 8 and as large litters as 15, disadvantageous combinations of large 

 litters borne by females with a few nipples cannot be of frequent occur- 

 rence. Commonly, there are about twice as many nipples (12) as 

 young (6). 



Experimental Parthenogenesis in Sea-urchins.* — M. Herlant 

 maintains (against Loeb, H indie, and Retzius) that the two poles of the 

 first mitosis in the parthenogenetic cleavage of the Echinoid ovum do 

 not result from the division of the female centrosome. The fact is that 

 the female centrosome, without dividing, forms one pole ; and the 

 other is a cytagter. The action of the hypertonic solution results in the 

 formation of a cytaster which secondarily enters into relations with the 

 monaster arising from the female pronucleus and its centrosome. A 

 perfect achromatin spindle is formed between them, and the chromosomes 

 form an equatorial plate. The opportune intervention of the cytaster 

 secures the transformation of the monaster, produced by activation, into 

 a bipolar mitosis. An abortive figure, incapable of leading to segment- 

 ation, is transformed into one which provokes segmentation and leads on 

 to the development of the egg. 



Studies on Germ-cells. f — Robert W. Hegner has studied germ-cells 

 (of insects in particular) with reference to the Keimbahn determinants, 

 that is to say, visible substances which are present in the egg before 

 cleavage begins, and later become part of the material contained in 

 the primordial germ-cells. The following events may be recognized 

 in the history of the Keimbahn determinants : — Localization of the 

 Keimbahn determinants in the oocyte or mature egg ; association 

 of one or more cleavage nuclei with part or all of the Keimbahn 



* Comptes Kendus, clix. (1914) pp. 408-10. 



t Journ. Morphol., xxv. (1914) pp. 375-499 (74 figs.). 



