Estep, P.W. (September 2010). Declining asexual reproduction is suggestive of senescence in hydra: comment on Martinez, D., "Mortality patterns suggest lack of senescence in hydra.". Experimental Gerontology. 45 (9): 645—6. doi:10.1016/j.exger.2010.03.017. PMID20398746.
Estep, P.W. (September 2010). Declining asexual reproduction is suggestive of senescence in hydra: comment on Martinez, D., "Mortality patterns suggest lack of senescence in hydra.". Experimental Gerontology. 45 (9): 645—6. doi:10.1016/j.exger.2010.03.017. PMID20398746.
Sergey Kuznetsov, Maria Lyanguzowa, Thomas CG Bosch / Role of epithelial cells and programmed cell death in Hydra spermatogenesis / Zoology, Vol. 104, Issue 1, 2001, Pages 25—31 PMID16351815