This is the basis on which female Ascaris can be identified

The correct option is straight posterior end.

Ascaris lumbricoides is a well-known roundworm that exhibits distinct sexual dimorphism, allowing clear differentiation between male and female worms based on external morphological features.

Here is a step-by-step breakdown of how a female Ascaris is identified and distinguished from a male:
1. Posterior End Shape: The most prominent diagnostic feature is the shape of the tail (posterior end). The female Ascaris has a straight, blunt, and pointed posterior end. In contrast, the male Ascaris has a curved posterior end that is bent ventrally.
2. Spicules and Papillae: Males possess a pair of curved chitinous structures called pineal spicules (or copulatory spicules) protruding from the cloacal aperture, along with numerous preanal and postanal papillae used during mating. Females lack these spicules and papillae.
3. Apertures: In males, the digestive tract and reproductive tract open together into a chamber called the cloaca, which exits through a cloacal aperture. In females, the anus and genital pore (vulva) are completely separate, so they do not have a common cloacal aperture.

Therefore, the presence of a straight posterior end is the correct basis on which a female Ascaris can be identified.