seminiferous tubule

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One of two or three twisted, curved tubules in each lobule of the testis in which spermatozoa develop.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy Any of many threadlike structures, located in the testes, that are the specialized areas of sperm production.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of the numerous long convoluted tubules in the testis which are the sites where spermatozoa mature