EXrERIMENTS ON SEX DETERMINATION. 435 



improbable that useful iuformation might be obtained from deter- 

 mining the relative position in the tube of foetuses of one or the 

 other sex. Records of the results obtained were indicated in the 

 form of a simple diagram, devised for the purpose. (Lantern - 

 slides of these Avere shown on the screen.) One point of interest 

 emerging from study of these diagi'ams is the frequent occurrence 

 of male couples. Whether these, as in tlie case of identical twins 

 in the human subject, are to be regarded as the outcome of 

 division of a single ovum could not be certainly determined. 



In a lecture on "Internal Secretion and the Ductless Glands" 

 by Dr. 8\vale Vincent (Lancet, Aug. 1, 190(5, footnote) Avill be 

 found a i*eference to a further outcome of this investigation, 

 personally communicated to him, "pointing distinctly to an in- 

 ternal secretion on the part of the interstitial cells " of the 

 testicle. Dr. Vincent notes that the " results are generally in 

 .agreement with those of Ancel & Bouin (Recueil de Medicine 

 Veterinaire, Jan. 15, 1904)." It became apparent also that in 

 the case of those rabbits in which the vas only was tied (with 

 careful exclusion of blood-vessels and nerves), the animals, as 

 contrasted Avitli those in which semi- castration had been per- 

 formed, showed no diminution of desire, or capacity, for sexual 

 intercourse ; while, on the average, they obtained larger families. 



The communication also included an experimental and critical 

 revieAv (illustrated by lantern-slides) of previous work on sex 

 determination by various obsei'vers whose investigations had 

 dealt with the study of this problem in plants, insects, and certain 

 of the lower vertebrates. 



Pkoc. Zool. Soc— 1919, No. XXX. 30 



