192 



Embryogenesis: Preparatory Phases 



the same cell, along with other evidence 

 from the literature of immunology, has sug- 

 gested an auto-antibody concept of cell struc- 

 ture, growth and differentiation, the details 

 of which are presented elsewhere (Tyler, 

 '40b, '42, '46b, '47). 



Lytic Agents. Sperm extracts of various 

 species of vertebrates and invertebrates have 

 been found to possess the property of break- 



(Tyler '39a, '48a; Krauss, '49). Evidence has 

 been obtained that its activity is dependent 

 upon the presence of sulfhydryl groups in 

 the molecule. 



Considerable attention has been paid in 

 recent years to the lytic agent in the sperm 

 extracts of mammals (see reviews by Duran- 

 Reynals, '42; Meyer, '47; Meyer and Rap- 

 port, '52). This agent causes dispersal of 



Fig. 62. Photomicrograph of an egg of Megathura crenulata at: a, 1 minute; t, 1% minutes; c, 2Yz minutes; 

 d, 3^ minutes after addition of a sperm extract containing the egg-membrane lysin. X 200. (From Tyler, 

 '39a.) 



ing down the membrane or viscous coat that 

 normally surrounds the unfertilized egg in 

 these species (see Hibbard, '28; Wintrebert, 

 '29, '33; Yamane, '30, '35; Pincus, '30, '36; 

 Tyler, '39a; Medem, '42). Figure 62 illus- 

 trates the action of such an agent on eggs 

 of the keyhole limpet. The dissolution of 

 the membrane (which can withstand hours 

 of treatment in- concentrated acid) can occur 

 in less than a minute in concentrated sperm 

 extracts containing the lytic agent. The ac- 

 tive agent has protein properties, is highly 

 heat-labile (about 1 minute half-life at 50° 

 C), and separable from the antifertilizin 

 present in keyhole limpet sperm extracts 



the follicle cells that normally surround the 

 unfertilized tubal egg, by dissolving the 

 cementing material between them. McClean 

 and Rowlands ('42) and Fekete and Duran- 

 Reynals ('43) showed that this was evi- 

 dently the same agent that was earlier shown 

 to have a dissolving action on the intercel- 

 lular cementing material of skin and that 

 had been designated hyaluronidase because 

 of its ability to break down the muco- 

 polysaccharide known as hyaluronic acid. 

 Hyaluronidase is also a heat-labile protein 

 and it has, as yet, been only partially puri- 

 fied (see Meyer, '47; Meyer and Rapport, 

 '52). The occurrence of this agent in vari- 



