Select the incorrect statement about external fertilisation.

Options

A. Organisms showing external fertilisation produce a large number of male gametes only.
B. External fertilisation is very uncertain and requires synchony between release of male and female gametes.
C. It is replaced by internal fertilisation in higher organisms as it wastes energy and requires external medium like water.
D. It occurs in most of the fishes and amphibians.

Explanation

To solve the question "Select the incorrect statement about external fertilization," we can follow these steps:

### Step 1: Understand External Fertilization
External fertilization occurs when the male and female gametes unite outside the body of the organisms. This process is common in aquatic animals like fish and amphibians.

**Hint:** Remember that external fertilization involves the release of gametes into the environment.

### Step 2: Analyze Each Statement
We will evaluate each statement provided in the question to determine which one is incorrect.

1. **Statement A:** "Organisms showing external fertilization produce a large number of male gametes only."
- This statement is incorrect because organisms that undergo external fertilization produce large numbers of both male and female gametes.

**Hint:** Think about the reproductive strategies of organisms that use external fertilization.

2. **Statement B:** "External fertilization is very uncertain and requires synchrony between the release of male and female gametes."
- This statement is correct. For successful fertilization, both gametes must be released at the same time.

**Hint:** Consider the timing and environmental factors that affect fertilization success.

3. **Statement C:** "It is replaced by internal fertilization in higher organisms as it wastes energy and requires an external medium like water."
- This statement is also correct. Many higher organisms have evolved to use internal fertilization for efficiency.

**Hint:** Reflect on the evolutionary advantages of internal fertilization over external fertilization.

4. **Statement D:** "It occurs in most of the fishes and amphibians."
- This statement is correct. Many fish and amphibians reproduce through external fertilization.

**Hint:** Recall examples of animals that reproduce externally.

### Step 3: Conclusion
After analyzing all the statements, we find that the incorrect statement about external fertilization is **Statement A**: "Organisms showing external fertilization produce a large number of male gametes only."

**Final Answer:** The incorrect statement is A.