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Gametogenesis, Fertilization and Parthenogenesis 



185 



ble of restoring normal membrane-forming 

 capacity to aged eggs. This may mean that 

 the rapid senescence of the unfertilized eggs 

 is due to loss (failure of resynthesis or un- 

 availability) of some such energy-transport- 

 ing agent. 



ATTACHMENT AND PENETRATION 



The specificity of fertilization is mani- 

 fested in the initial steps of the union of the 

 gametes. In general spermatozoa will not 

 adhere to, or penetrate, eggs of other spe- 

 cies or other tissues of the same species. 

 Some exceptions to this are known. Thus 

 sperm of the nemertean worm Cerebratulus 

 penetrate eggs of the sand dollar Echinarach- 

 nius (Chambers, '33). The sperm remain in 

 the cortex without activating the egg, which 

 can subsequently develop normally upon fer- 

 tilization with the species sperm. Instances 

 of penetration of sperm into tissvie cells have 

 been less frequently reported (see Terni 

 and Maleci, '37). In view of the marked 

 specificity and the superficial resemblance 

 to phagocytosis it is not surprising that the 

 first detailed modern theory of fertilization, 

 namely that of F. R. Lillie ('19), should be 

 based on immunological analogies. This was 

 undoubtedly favored, too, by the discovery 

 (Lillie, '12, '13a, b) that spermatozoa of 

 certain marine animals can be made to ag- 

 glutinate by the addition of some egg water 

 (supernatant of a suspension of eggs) of 

 the same species. The agglutinating sub- 

 stance in the egg water was termed fer- 

 tilizin and Lillie assigned it a central role 

 in his theory of fertilization. The early work 

 in this field has been reviewed by Lillie 

 ('19), Lillie and Just ('24), Morgan ('27), 

 Dalcq ('28b) and Just ('30). The present 

 discussion will be based mainly on the more 

 recent work, which has been reviewed in 

 some detail by Tyler ('48a, '49), Bielig and 

 Medem ('49), and Rvmnstrom ('49). 



We shall consider four groups of inter- 

 acting substances that have been obtained 

 from eggs and sperm and which are termed 

 fertilizins, antifertilizins from sperm, anti- 

 fertilizins from eggs, and lytic agents from 

 sperm. The terms gynogamone and andro- 

 gamone were introduced by Hartmann 

 ('40) to designate the substances derived 

 from eggs and sperm, but this terminology 

 does not seem to be any less prejudicial than 

 that of Lillie, nor sufficiently advantageous 

 to warrant its adoption. 



Fertilizins. Agglutination of sperm by ho- 

 mologous egg water has been reported in 



many species of animals among the echino- 

 derms, annelids, molkisks, tunicates and ver- 

 tebrates (see Tyler, '48a, and Bielig and 

 Medem, '49, for references). The reaction in 

 strong egg water is usually visible within a 

 few seconds. In sea urchins the clumping 

 is ordinarily head to head (Lillie, '19; Elster, 

 '35). Tail to tail and head to tail, along 

 with head to head unions have been re- 

 ported in certain mollusks and may occur 

 also in aged sea urchin sperm (Sampson, 

 '22; Tyler, '40a). Figures 56 to 58 illus- 

 trate the agglutination reaction of sperm of 

 the keyhole limpet Megathura crenulata. 

 The reaction is similar in appearance to 

 that exhibited by sperm that are aggluti- 

 nated by an immune serum (compare figures 

 of Henle et al., '38). The reaction also ex- 

 hibits such serological features as the zone 

 phenomenon (Tyler, '40a; Spikes, '49a). Lil- 

 lie ('19) used the term fertilizin to designate 

 the agent or agents in egg water that were 

 responsible for agglutinating, activating and 

 possibly chemotactic and other effects. At 

 present it seems best to restrict the use of 

 this term to the agglutinin. 



A unique feature of the reaction in sea 

 urchins is its spontaneous reversal after a 

 period of time ranging from a few seconds 

 in dilute egg water to many minutes in con- 

 centrated egg water, whereas in other groups 

 of animals the agglutination is essentially 

 permanent or long-lasting. Following spon- 

 taneous reversal, in the sea urchin, the 

 spermatozoa are incapable of being re- 

 agglutinated by the addition of fresh egg 

 water and have lost their fertilizing capacity, 

 although they are fully motile (Lillie, '19; 

 Tyler, '41). An interesting analogy to this 

 is found in the Hirst ('42) reaction of ag- 

 glutination of vertebrate red blood cells by 

 influenza, and other viruses. This reaction 

 also reverses spontaneously and the red cells 

 are incapable of re-agglutination. In the case 

 of the sea urchin the reversal has been in- 

 terpreted (Tyler, '41) as due to a splitting 

 of the individual fertilizin molecules that 

 bind the spermatozoa to one another. This 

 interpretation presumes that the now gen- 

 erally accepted mutvial multivalence theory 

 of antigen-antibody reactions (Heidelberger, 

 '38, '39; Marrack, '38; Pauling, '40) holds 

 for the agglutination of sperm by fertilizin. 

 According to this theory both antigen and 

 antibody must be multivalent with respect 

 to their combining groups in order for their 

 interaction to result in precipitation or ag- 

 glutination. In other words, an agglutinin 

 molecule must possess two or more combin- 



