प्लेसेंटा (अपरा) का भ्रूणीय भाग मुख्य रूप से किससे व्युत्पन्न होता है?

In which of the following embryonic stages of development does the blastocoel develop?

Which cell movement process is primarily responsible for initiating the formation of the primitive streak during avian and mammalian gastrulation?

During the embryonic development of a frog, the blastopore first appears during the: