Such an ovum as that of our present type, however being devoid of such yolk (alecithal = without yolk), necessitates a very early start in life, and, for reasons too complicated to state fully here, the development in such a case is considered particularly instructive and primitive by zoologists.    From Wordnik.com.  [Text Book of Biology, Part 1: Vertebrata] Reference

(alecithal), and, therefore, we find it dividing completely and almost equally.    From Wordnik.com.  [Text Book of Biology, Part 1: Vertebrata] Reference