Species richness- which is a count of the number of species.

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#Id: 1029

#Unit 5. Developmental Biology

There are two principal modes of neurulation: 

1. Primary neurulation

2. Secondary neurulation

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#Id: 1030

#Unit 5. Developmental Biology

In primary neurulation, 

cells surrounding the neural plate direct the neural plate cells to proliferate, invaginate into the body, and separate from the surface ectoderm to form an underlying hollow tube.

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#Id: 1031

#Unit 5. Developmental Biology

In secondary neurulation, 

the neural tube arises from the aggregation of mesenchyme cells into a solid cord that subsequently forms cavities that coalesce to create a hollow tube.

 

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#Id: 1032

#Unit 5. Developmental Biology

Primary neurulation forms the anterior portion of the neural tube

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#Id: 1033

#Unit 5. Developmental Biology

Secondary neurulation forms the posterior portion of the neural tube 

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#Id: 1034

#Unit 5. Developmental Biology

In birds, primary neurulation generates the neural tube anterior to the hindlimbs.