Vertebrate Embryology, January 25, 2013, Albert K. Harris   Yolk amount and concentration: Effects on cleavage patterns and gastrulation   Sea Urchin Amphibian Bird + Reptile Mammal Teleost Fish       less yolk more yolk (concentrated near vegetal pole) very large amount of yolk less yolk very much yolk       equal cleavage unequal cleavage meroblastic cleavage   equal cleavage meroblastic       gastrulate by invagination (and some ingression)   gastrulate by involution gastrulatealong primitive streak   by ingression gastrulate along primitive streak by ingression epiboly       back to syllabus