318 SUMMARY OF CURRENT RESEARCHES RELATING TO 



canal in sheep embryos. He adds a discussion of the tail in human 

 embryos. Finally he homologizes with the embryonic caudal thread, 

 the soft coccygeal appendix of Inuus pithecus, and similar structures 

 found abnormally in the chimpanzee, orang-outang, and man, and 

 gives citations to prove that the caudal thread exists in human 

 embryos. 



Influences which Determine Sex in the Embryo* — Prof. E. 



PflUger publishes at length an account of experiments, performed 

 with the greatest care, with the object of throwing light upon some 

 of the most prominent of the obscure problems of the physiology of 

 generation. He made use of frogs in his exjjeriments ; many 

 hundreds of the creatures were obtained from various neighbourhoods, 

 and were maintained while under observation under conditions made 

 as nearly normal as j)ossible. 



The first question dealt with is : Does the concentration of the 

 spermatic fluid of the male influence the sex of the ofispring ? Much 

 care is necessary in handling frogs' eggs, for they are exceedingly 

 susceptible of mechanical injury. The pair of frogs are parted 

 during the sexual embrace, and therefore at a time when the products 

 of the generative organs are presumably ripe, the animals are killed, 

 and the spermatic sacs of the males are emi)tied into a watch-glass. 

 A second watch-glass, filled with water, is impregnated with sper- 

 matozoa by dipping into it the tips of the fine pair of scissors which 

 has just been used to cut open the si)ermatic sacs and has, therefore, 

 some of their contents clinging to it. The dilute spermatic fluid of 

 the second watch-glass was often further diluted from ten to twenty 

 volumes, and from these new mixtures fresh quantities of water in 

 watch-glasses were impregnated by the transference of a film of fluid 

 clinging to the scissors' tips. Into these watch-glasses, filled with 

 the fluid of a single male in dififerent states of concentration, there 

 were allowed to glide some of the eggs of the female taken from the 

 right uterus. 



The experiments established two facts, first, the fertilizing power 

 of the spermatic fluid was not diminished by dilution, all the ova 

 were fertilized in each observation ; second, dilution of the male 

 fluid had no efiect on the sex of the frogs which came to maturity 

 after the artificial fertilization. 



In young frogs there are three varieties of sexual character, male, 

 female, and hermaphrodite. The hermaphrodites become finally either 

 male or female, but in their earlier stages they have the sexual organs 

 of the female only ; in those which are finally to become males, the 

 testicles gradually develop round the ovaries and the latter are 

 resorbed. This apparent numerical predominance of the female in 

 early stages of the fuller formed frog has led some investigators 

 astray. 



The author finds that no Batrachian egg segments without previous 

 fertilization. The fertilizing power of the male fluid diminishes 

 greatly and progressively after the season for sexual union. 



* Pfluger'e Archiv, xxix. Cf. Amer. Natural., xvii. (18S3) pp. 441-2. 



