Find out the incorrect statement w.r.t. frog-

Options

A. Only tympanum can be seen externally
B. Columnae carnaeae are present in ventricle
C. bidder's canal communicates with the oviduct
D. vasa efferentia are 10-12 in number

Explanation

### Step-by-Step Solution:

1. **Identify the Statements**: The question requires us to find the incorrect statement regarding frogs. We have four statements to evaluate.

2. **Evaluate the First Statement**:
- The first statement claims that "only tympanum can be seen externally."
- The tympanum is indeed the external ear of the frog, and frogs do not have an external ear structure like a pinna.
- **Conclusion**: This statement is correct.

3. **Evaluate the Second Statement**:
- The second statement states that "columnar carni are present in the ventricle."
- Frogs have a three-chambered heart, which includes two atria and one ventricle. The ventricle contains muscular columns known as columnar carni.
- **Conclusion**: This statement is also correct.

4. **Evaluate the Third Statement**:
- The third statement claims that "Bidder's canal communicates with the oviducts."
- Bidder's canal is part of the male reproductive system in frogs and is responsible for transporting sperm from the testis. It does not communicate with the oviducts, which are part of the female reproductive system.
- **Conclusion**: This statement is incorrect.

5. **Evaluate the Fourth Statement**:
- The fourth statement says "vas aferentia are 10 to 12 in number."
- Vas aferentia are indeed the structures that transport sperm to Bidder's canal, and they are typically found in numbers ranging from 10 to 12.
- **Conclusion**: This statement is correct.

6. **Final Answer**: The incorrect statement regarding frogs is that "Bidder's canal communicates with the oviducts."