Thymus
The thymus was a gland located in the upper  of a Human body. It played an important role in the Human immune system.

The parasitic Tarchanne s were located in the thymus after infecting a host, using the immune system to spread genetic instructions that would turn the host into a full member of the species. 

Doctor Beverly Crusher successfully removed the parasite from Susanna Leijten's and Geordi La Forge's thymuses after they were infected by the lifeform. ()

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Glands