Some species are ovoviviparous and the young develop internally but others are oviparous and the larvae develop externally in egg cases.
sˌʌm spˈiːsiːz ɑːɹ ˈoʊvəvˌɪvɪpɚɹəs ænd ðə jˈʌŋ dɪvˈɛləp ɪntˈɜːnəli bˌʌt ˈʌðɚz ɑːɹ ˈoʊvɪpɚɹəs ænd ðə lˈɑːɹviː dɪvˈɛləp ɛkstˈɜːnəli ɪn ˈɛɡ kˈeɪsᵻz.