Which are not homologous?

Options

A. Forearms of humans and fins of fishes
B. Wings of bat and insects
C. Fins of fishes and flippers of whales
D. Human forearms, bat's wings, and flippers of whale

Answer

To determine which organs are not homologous, we first need to understand the concept of homologous and analogous structures.

### Step-by-Step Solution:

1. **Define Homologous Structures**: Homologous organs are those that have the same basic structure but may serve different functions. For example, the forelimbs of humans and the wings of bats are homologous because they share a similar bone structure despite serving different purposes (manipulation vs. flying).

2. **Define Analogous Structures**: Analogous organs, on the other hand, perform similar functions but have different structures. An example is the wings of bats and the wings of insects. They both allow for flight but are structurally different.

3. **Analyze the Options**:
- **Option 1**: Flippers of whales and fins of fishes - These are homologous because they share a common ancestor and have similar bone structures.
- **Option 2**: Wings of bats and wings of insects - These are analogous because they perform the same function (flight) but have different structures.
- **Option 3**: Forelimb of humans and fins of fishes - These are not homologous; they are analogous because they serve different functions.
- **Option 4**: Co-appendages of crabs - These are homologous as they share a common structure with other arthropods.

4. **Identify Non-Homologous Structures**: From the analysis, the non-homologous structures identified are:
- **Forelimb of humans and fins of fishes** (analogous)
- **Wings of bats and wings of insects** (analogous)

5. **Conclusion**: The pairs that are not homologous are the forelimb of humans and fins of fishes, as well as the wings of bats and wings of insects.

### Final Answer:
The structures that are not homologous are the forelimb of humans and fins of fishes.