EMBRYOLOGY LECTURE NOTES -3
DIFFERENT TYPES OF BLASTULA
The blastula of various groups of animals differs in form and structure depending upon a variety of
factors such as the size of the amount and distribution of yolk etc. The following categories of
blastulae have been recognized in different groups of animals.
1 Coeloblastula
It is a hollow blastula containing a large spacious blastocoel. Usually, the blastocoel is filled with a
fluid containing mucopolysaccharides. The blastula resulting from holoblastic equal ceavage, as in
the case of echinoderms and amphioxus, is called equal coeloblastula . ln this case, the blastoderm is
single layered. Holoblastic unequal cleavage, as in frog, results in unequal coelobtastuta. lt has a
blastocoel displaced towards the animal pole and a multilayered blastoderm.
2. Stereoblastala
This type of blastula is composed of an aggregate of larger sized and relatively lesser number of
cells without or with extremely small blastocoelic space in the centre. Stereoblastula occurs in a
variety of animals such as insects, some worms like Nereis, mollusks like Cripidula, gymnophionan
amphibians and certain fishes.
3. Discoblastula
Discoblastula consists of a disc - shaped mass of blastomeres overlying a large yolk mass. This
blastula is the result of meroblastic discoidal cleavage as in most fishes, reptiles and birds. There is
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DIFFERENT TYPES OF BLASTULA
The blastula of various groups of animals differs in form and structure depending upon a variety of
factors such as the size of the amount and distribution of yolk etc. The following categories of
blastulae have been recognized in different groups of animals.
1 Coeloblastula
It is a hollow blastula containing a large spacious blastocoel. Usually, the blastocoel is filled with a
fluid containing mucopolysaccharides. The blastula resulting from holoblastic equal ceavage, as in
the case of echinoderms and amphioxus, is called equal coeloblastula . ln this case, the blastoderm is
single layered. Holoblastic unequal cleavage, as in frog, results in unequal coelobtastuta. lt has a
blastocoel displaced towards the animal pole and a multilayered blastoderm.
2. Stereoblastala
This type of blastula is composed of an aggregate of larger sized and relatively lesser number of
cells without or with extremely small blastocoelic space in the centre. Stereoblastula occurs in a
variety of animals such as insects, some worms like Nereis, mollusks like Cripidula, gymnophionan
amphibians and certain fishes.
3. Discoblastula
Discoblastula consists of a disc - shaped mass of blastomeres overlying a large yolk mass. This
blastula is the result of meroblastic discoidal cleavage as in most fishes, reptiles and birds. There is
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