After such a long vowel homogenous with the first, n is substituted for the s of the Acccusative case affix śas in the masculine.,
Thus वृक्ष + शस् = वृक्ष + अम् = वृक्षान् ॥ So also अग्नीम्, वायून्, कर्तॄन्, होतॄन्, पण्डकान्, स्थूरान्, अरकान्, पश्य &c. All these are masculine nouns. Now the word चञ्चा formed by the elision of कन् meaning a figure like a चञ्चा 5.3.98, may refer to both the males and females. It will however retain its feminine form though referring to a male being (See लुपि युक्तवद् व्यक्ति वचने (1.2.51). In forming the accusative plural of चंचा, the स् will not be changed into न् ॥ Thus चंचाः पश्य, वध्रिकाः पश्य ॥ Why do we say 'after such a long vowel homogenous with the first'? The rule will not apply if the long vowel has resulted by being a single substitute for the antecedent and the subsequent. Thus आ is substituted for ओ + अ by 6.1.93. Here स् will not be replaced by न् as गाः पश्य ॥ Why do we say 'of the Accusative plural'? Observe वृक्षाः, प्लक्षाः endings in जस् Nominative Plural. Why do we say \in the masculine?\ Observe, धेनुः, बह्वीः, कुमारीः ॥,