DEGENERATE SEXUAL REPRODUCTION. I59 



extended, and thought over by naturalists of the standing of Owen 

 (1843), Von Siebold (1856), and Leuckart (1858), whose conclusions 

 have afforded a firm basis for the abundant subsequent observation 

 and speculation of this interesting subject. 



II. Degrees of Parthenogenesis. — If we start, then, with 

 Von Siebold" s definition of parthenogenesis, as the power possessed 

 by certain female animals of producing offspring without sexual 

 union with a male, it will clear the ground to notice, in the first 

 place, the numerous different degrees in which this development 

 without fertilization may occur. 



{a) Artificial Partlicnogaicsis. — There are a few curious obser- 

 vations which go to show that in exceptional circumstances ova may 

 develop when the male stimulus is replaced by some artificial reagent. 

 These observations must still be taken cum grano salis, but they may 

 be at least suggestive of further experiment. Dewitz observed unfer- 

 tilized frog-ova to undergo segmentation [sic] in corrosive sublimate 

 solution. In some cases one division occurred, in others several; in 

 some cases irregularly, in others normally. It happened both when 

 the ova were left in the reagent, and when they were merely dipped 

 and returned to water. The eggs experimented on were those of the 

 two common frogs Rana fusca and R. esculenta, and of the tree-frog 

 {Hyla arborca). But it must be noted that Leuckart long ago 

 noted the occurrence of spontaneous division in frog ova. Similarly, 

 Tichomiroff, experimenting with the unfertilized ova of the silkmoth, 

 which are occasionally parthenogenetic, was surprised to observe that 

 ova, which would not of themselves develop parthenogenetically, 

 might be induced to do so by certain stimuli. These consisted in 

 rubbing the unfertilized ova with a brush, or in dipping them for 

 two minutes in sulphuric acid and then washing them. In both cases, 

 he says, a percentage of the ova thus artificially stimulated developed. 

 It must be remembered that occasional parthenogenesis occurs in this 

 insect, and all that Tichomiroff did was to incite this. There is 

 no doubt that reagents may considerably modify ova; thus the 

 brothers- Hertwig showed how it was in this way possible to over- 

 come the non-receptivity of the ovum to more than one sperm. Nor 

 can one forget how sexual reproduction in parasitic fungi tends to 

 disappear, being apparently replaced by the stimulus afforded trom the 

 waste products of the host. In a similar way, the multiplication of 

 cells, so frequently associated in disease with the presence of bacteria, 

 has been referred by more than one pathologist to the "sper- 

 matic influence" of these micro-organisms, or of the katastates which 

 they form. 



