s or ṣ is substituted for the visarga before a hard guttural or a labial in the words kaska etc.,
This is an Apavada to Sutra 8.3.37. ष् is substituted after इ or उ, and स् everywhere else. Thus कस्कः, 2. कौतस्कुतः (with अण् of कुत आगतः). 3. भ्रातुष्पुत्रः 6.3.23 4. शुनस्कर्णः 6.3.21 5. सद्यस्कालः; 6. सद्यस्क्री (from क्री 'to buy' with the affix क्विप्, because it belongs to Sampadadi class.) 7. साद्यस्क्रः (from सद्यस्क्री in the sense of तत्रभवः क्रतुः). 8. कांस्कान् (the रु is by 8.3.12). 9. सर्पिष्कुण्डिका, 10. चतुष्कपालम्, 11. धनुष्कपालम् 12. बर्हिष्पूलम्, 13. यजुष्पात्रम् ॥ \The words 9 to 13 are exceptions to 8.3.45, so that there might be ष, even when सर्पिस् &c are preceded by another word. Thus परमसर्पि ष्कुण्डिका ॥ The counter-example then to 8.3.45 will be परमसर्पिः फलम् ॥ \This is the opinion of the Parayanikas. But in the Mahabhashya, the counter-example under 8.3.45 is परमसर्पिः कुण्डिका ॥ Another reason why these words are listed here, is that ष change will take place, even where there is no correlation or vyapeksha. As तिष्ठतु सर्पिष्कुण्डिकां आनय ॥ So also when there is correlation, as इदं सर्पिष्कुण्डिकायाः ॥ Here सर्पिस् is an incomplete word. The ष change, will take place even where there is no compounding. Where there is no compounding, and there is complete want of correlation, even there the ष will invariably come. And where there is correlation, but no compounding there the ष would have been optional by 8.3.44, but it becomes invariable here, on account of these words being so listed. Thus we have these cases : (1) Without correlation, as तिष्ठतु सर्पिष्कुण्डिकामानय ॥ (2) Where there is correlation, as इदं सर्पिष्कुण्डिकायाः ॥ (3) Where there is composition, as सर्पिष्कुण्डिका ॥ (4) Where there is no composition and no correlation even, as, in example (1). (5) Where there is correlation but no compounding as in example (2). In all these cases there ष is invariably in case of these words. 14. अयस्काण्डः, 15. मेदस्पिण्डः ॥ अविहितलक्षण उपचारः कस्कादिषु द्रष्टव्यः ।
Every change of visarga to स or ष, must be referred to Kaskadi class, is not governed by any other rule. Thus this is an Akrtigana. Upachara is the name of स् and ष् which replace the visarga.
The Parayana is of two sorts, Dhatu-Par, and Nama-Par. Those who devote themselves in committing to memory and reciting these are Parayanikas.,