Final answer:
The presence of seminal vesicles alone does not determine the sex of an earthworm.
Step-by-step explanation:
The presence of seminal vesicles alone on a lab slide does not definitively indicate the sex of an earthworm. Earthworms are hermaphroditic, meaning they have both male and female reproductive organs. The seminal vesicles are part of the male reproductive system and produce semen, but they can be present in both male and female earthworms. To determine the sex of an earthworm, additional reproductive structures and characteristics need to be observed.