SPECIFICITY 139 



clusively determined by the fertilizin-antifertilizin reaction. On 

 the other hand, Table 22 shows that in general, cross-fertilization 

 implies cross-agglutination. Even in the apparently exceptional 

 cases of eggs or fertilizin from Strongylocentrotiis franciscanus (A. 

 Agassiz) or spermatozoa from Strongylocentrotiis purpuratiis and 

 Dendr aster excentricus (Eschscholtz), Tyler has shown that sperm- 

 atozoa of the latter cchinoderms do combine with fertilizin of the 

 former. 



The partially successful interphyletic crosses which have been 

 achieved, such as Strongylocetitrotiis $ X Mytilus <S (Kupelwieser, 

 1909), raise a number of interesting but difficult problems, p will 

 clearly be very low in such cases ; but there is no particular reason 

 why a successful hit should not be achieved from time to time, 

 even if subsequent development is gynogenetic. Kupelwieser's 

 experiments do not exclude an alternative possibility: that such 

 crosses can be achieved without specific adhesion between the 

 surfaces of the egg and the spermatozoon, but as a result of the 

 action of a non-specific lysin or detergent-like compound, diffusing 

 out of the sperm head and softening up the egg cortex so that the 

 sperm can be readily engulfed. F. R. Lillie (1919) favoured this 

 interpretation of Kupelwieser's results, and there have been refer- 

 ences elsewhere in this book to the possibility of misinterpreting 

 experiments involving insemination with very high sperm con- 

 centrations, because of the possibility of non-specific effects due to 

 sperm lysins or A. III. But even if, intuitively, we do not like the 

 idea of there being a sufficient degree of complementariness be- 

 tween the surface of eggs and spermatozoa of different phyla to 

 permit activation, we must still admit that the possibility exists, 

 first because the 'fit' does not have to be complete (see later in this 

 chapter), and secondly, because the reaction is essentially a proba- 

 bilistic one, in which p does not equal zero. Whatever one's in- 

 tuitive feelings may be, cross reactions do occur: a classical ex- 

 ample is the Weil Felix Reaction, in which B.proteus is agglutinated 

 by serum from patients with typhus ! - 



Apart from certain examples and analogies, what has been said 

 above about specificity is mainly empirical, or analytical, in the sense 

 of being based on the laws of probability and the kinetic theory of 

 gases. When we come to examine the 'how' part of the problem, 

 almost complete ignorance prevails, in spite of the immense number 

 of cross-fertilization experiments which have been done during 



