i8o COMPARATIVE PHYSIOLOGY 



Arbacia, and this reaction is an irreversible and toxic effect, 

 unlike the reversible reaction of the sperm to egg-secretion of 

 the same species. According to Lillie's experiments the 

 ** iso " — and *' hetero " — agglutinating reagents are different 

 substances. He infers this from two lines of evidence : (i) that 

 egg-water of Arbacia, which originally acted on the sperm of 

 both genera, on keeping lost its action upon the eggs of Nereis 

 while retaining its activity with reference to sperm of the same 

 species ; and (2) after removal of all the agglutinating substance 

 which affects Nereis sperm by addition of the Arbacia egg- water 

 to a sperm-suspension of Nereis, the agglutinating action of 

 the egg-secretion on Arbacia or Arbacia sperm was unimpaired. 

 It was also found that the sperm of a Teleost would neutraUse 

 the hetero-active substance. While these phenomena provide 

 new materials for the serologist, it is perhaps premature to 

 emphasise very strongly the conclusion stated by Lillie that 

 " egg substances that thus activate and direct specific 

 spermatozoa and render them adhesive are well suited to 

 favour the fertilisation reaction." 



Such information as is available with reference to the 

 specificity of the fertilisation act does not lead to very definite 

 conclusions. The sperm of one species will not in general 

 fertilise the eggs of another species. But this specificity 

 is not by any means absolute, and as illustrated by the rather 

 extreme example of Kupelwieser's experiment, it can be 

 overcome to some extent by experimental manipulation. 

 When this can be done it is possible to search for some factor 

 which specially distinguishes the normal process from the 

 experimental procedure. The problem still remains to be 

 solved. Baltzer, Tennent, Shearer, de Morgan and Fox, 

 Fischel, and others have successfully hybridised different 

 species and genera of Echinoderms ; similar experiments have 

 been made on Teleosts by Newman and Moenkhaus, and on 

 Amphibia by Bataillon. 



Careful investigations into this phenomenon by Fox (19 16) 

 on Ciona failed to throw very much light on the question. 

 Ciona exhibits an interesting form of specificity, one that may 

 be common among hermaphrodite organisms and does not 



