Kev loj hlob tsis ncaj yog tus yam ntxwv ntawm invertebrates, mollusks thiab amphibians. Hauv qhov no, embryo muaj qhov sib txawv tseem ceeb piv rau cov neeg laus tsiaj. Ua piv txwv, npauj npaim zoo tib yam yog qhov tsim nyog. Tsuas yog tom qab ob peb theem ntawm txoj kev loj hlob tau dhau mus, cov larva me me yuav hloov dhau qhov kev lees paub