Zoology Answers

Could you tell me what does extensive in the following paragraph means?

Diffuse placenta:

Among primates (lemurs) and some ungulates (pig, horse), the chorionic villi remain scattered all over the surface of the chorion and their placentae are correspondingly extensive.

I was reading Developmental biology of chick, the formation of yolk sac and stumbled upon the presence of two vitelline arteries along with vitelline veins. The function of vitelline veins is to transport the digested yolk sac material to the growing embryo but what's the role of its arterial counter part?

The yolk doesn't need oxygen, they are not living tissues. Could it be the yolk sac cells that the arteries are providing O2 to?

Fertilizin-antifertilizin reaction lead to agglutinisation of sperms. How would it at all help in fertilisation process? Won't it actually hinder the sperm from fertilising?

What actually determines the location of blastopore formation in amphibians at molecular level?
Well I know blastopore develops in the region just below the gray crescent(from Developmental biology Gilbert), a place virtually opposite to the point of entry of sperm. But I want to know why this place get chosen?
Has there been any discovery in this regard? Please give me some hint and I'll do the rest of the research.

I can't find a detailed illustrative discussion on Gastrulation of frog in any of the highly recommended books like Gilbert and Wolpert. All I've found is a book called Simplified Course In Bsc Zoology Chordate Embryology And Histology that though has a detailed explanation on this topic but after reading it I'm left with several questions like-

1. What happens to the inner cell mass of blastula? What's its fate?
2. Are the presumptive mesodermal cells present as a part of blastoderm?
3. What decides the anterior-posterior axis of frog embryo?

I've thoroughly searched the google.books and google.com with no luck, where can I find a good book or a paper explaining the mentioned topic. It would be great if the explanation does deep into the molecular level.

I was looking for the importance of fate maps so I did some normal google.book search and found the following two importance of fate maps-

1. They helped establish the idea that communication between different parts of an embryo leads to the formation of new cell types and have thus helped discover different signalling pathways.

2. They enable us to interpret experiments in which cells of the embryo are exposed to conditions that may alter their developmental fate.

But I don't know how to find some experiments in which fate maps were really helpful in the mentioned ways.Besides are there other ways in which fate maps have helped our understanding of development? I'll be really grateful if you could tell me, how and where do I look for some sample experiments ?