exists and is an alternate of . The sperm that reach the egg swim into it and attempt to penetrate the zona pelluca, which is the semi permeable outer membrane of the egg. Some sperm have a shape which makes this relatively easy, and others which are poorly formed are likely to have more difficulty.
1 Shigellosis is an infectious disease caused by a group of bacteria called Shigella. 2  Symptoms of Shigella infection include diarrhea (often bloody), fever, and stomach cramps starting a day or two after exposure to the bacteria. 3  Shigellosis usually resolves in 5 to 7 days.
For the disease, see shigellosis. For the toxin that is produced by certain strains of Shigella and E. coli bacteria, see Shiga toxin. Shigella (/ÊÉªËÉ¡ÉlÉ/) is a genus of Gram-negative, facultative anaerobic, non-spore-forming, non-motile, rod-shaped bacteria closely related to Salmonella.The genus is named after Kiyoshi Shiga, who first discovered it in 1897.higella species are classified by four serogroups 1  : Serogroup A: S. dysenteriae (15 serotypes). 2  Serogroup B: S. flexneri (six serotypes). 3  Serogroup C: S. boydii (19 serotypes). 4  Serogroup D: S. sonnei (one serotype).