During cleavages, differnt cleavage furrows may divide the egg from different planes. Few important cleavage planes are following: 1. Meridional plane- When cleavage furrow passes through the centre of animal-vegetal axis and bisects the both poles of the egg, then such plane of cleavage is called meridional plane, e.g., Rana pipiens, Lepidosteus osseus and first [...]
The rate of cleavage varies from species to species. For example, in the gold fish, divisions follow each other continuously at regular intervals of 20 minutes. The inter-cleavage interval of frog is one hour and of mouse is 10 to 12 hours. In most of these cases, the cleavage rate remains rapid (synchronous) during completion [...]
Though, the mitosis involved in cleavage and the mitosis occurred in late embryos and in adult animals, is fundamentally same, but, both differ in following aspects: 1. In the later embryonic stages and in the adult, the mitosis is intimately connected with growth. After each mitotic cell division the daughter cells grow and when they [...]
The process of cleavage could be noticed to be operative in animal eggs, only in the eighteenth century, when, in year 1738 first of all Swammerdam observed the first cleavage of the frog’s egg. In 1780, Spallanzani described first two cleavage planes of egg. Prevost and Dumas in 1824, made extensive observations on the cleavage [...]
This is the inherent nature of the sexually reproductive multi-cellular animals that their body originates from a large-sized, single celled (unicellular), nutrient-filled, diploid and fertilized egg or zygote. In them, immediately after the activation of egg either through the intervention of a spermatozoon (fertilization) or through some parthenogenetic agent (parthenogensis), the activated egg is passed [...]
