sex gland vs ovotestis

sex gland and ovotestis both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex gland	Yes	No	No	No
ovotestis	Yes	No	No	No

As nouns, ovotestis is a hyponym of sex gland; that is, ovotestis is a word with a more specific, narrower meaning than sex gland:

sex gland: a gland in which gametes (sex cells) are produced
ovotestis: hermaphroditic gonad that contains both testicular and ovarian tissue

Other hyponyms of sex gland include ovary, ball, ballock, bollock, egg, nut, orchis, testicle, testis.

sex gland (noun)	ovotestis (noun)
a gland in which gametes (sex cells) are produced	hermaphroditic gonad that contains both testicular and ovarian tissue