What evidence led ruth and sessions to conclude that parasites could be the cause of some of the deformities in the frogs found in ponds of northern california?

The frogs in a pond experience the same abnormality.

A resin bead used to copy the cysts formed by parasites resulted in extra limbs.

Explanation:

Ruth S.B and Sessions S.K carried out an experiment to determine the common occurrence of abnormal limb growth in frogs. They discovered that a parasite, the flatworm found in ponds is responsible for the abnormality. These parasites form cysts and when they infect a growing frog, the cysts may stop the growth of limbs that have already started to grow.

The frogs generate new limb tissue, thereby causing new limbs or digits to grow and resulting in multiple digits or limbs

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sounds good to me mate!

you answered your own : -/