Can be classified and solved.

(1) 6 people were admitted.

Can be divided into three categories.

① 4+ 1+ 1，C(6，2)*A(3，3)= 15*6=90

② 3+2+ 1，C(6，3)C(3，2)*C( 1， 1)*A(3，3)=360

③ 2+2+2 C(6，2)*C(4，2)*C(2，2)/A(3，3) *A(3，3)=90

There are 540 such cases.

(2) Admission of 5 people.

Choose five people first, c (6,5) = 6.

And then divided into two categories.

① 3+ 1+ 1，C(5，3)*A(3，3)= 10*6=60

② 2+2+ 1，C(5，2)C(3，2)*C( 1， 1)/A(2，2) *A(3，3)=90

In this case, there are 150*6=900 kinds of * *.

(3) admit 4 people.

Choose four people first, c (6,4) =15.

And then divided into one category.

① 2+ 1+ 1，C(4，2)*A(3，3)=6*6=36

In this case, there are 15*36=540 * *.

(4) admit three people.

Choose three people first, c (6,3) = 20.

And then divided into one category.

① 1+ 1+ 1，A(3，3)=6

In this case, * * has 20*6= 120.

Based on the principle of classified counting,

* * * There are 540+900+540+120 = 2100 species.