Charak Samhita
गर्भस्तु खल्वन्तरिक्षवाय्वग्नितोयभूमिविकारश्चेतनाधिष्ठानभूतः। एवमनया युक्त्या पञ्चमहाभूतविकारसमुदायात्मको गर्भश्चेतनाधिष्ठानभूतः; स ह्यस्य षष्ठो धातुरुक्तः ॥६॥
[Composition of embryo] Garbha (embryo) is produced by the five mahabhutas, i.e. akasha,vayu, agni, jala and prithvi and associated with the consciousness (chetana). It represents the combination of five mahabhutas and is also a holder of consciousness. Thus, the chetana constitutes the sixth dhatu and is responsible also for the formation of garbha (embryo).
english translation
garbhastu khalvantarikSavAyvagnitoyabhUmivikArazcetanAdhiSThAnabhUtaH। evamanayA yuktyA paJcamahAbhUtavikArasamudAyAtmako garbhazcetanAdhiSThAnabhUtaH; sa hyasya SaSTho dhAturuktaH ॥6॥
hk transliteration by Sanscript