Just one reason :)
2007-04-23 15:57:03 · 4 answers · asked by MJ 1 in Science & Mathematics ➔ Biology
Shells?
2007-04-23 16:34:39 · answer #1 · answered by Anonymous · 0⤊ 0⤋
Fertilization must happen before the egg gets a shell.
2007-04-23 16:17:49 · answer #2 · answered by ecolink 7 · 0⤊ 0⤋
-one reason being because they cannot give birth to babies as the way of "marsupial" animals do, in which the embryo is born at a very early stage of development (at about 4-5 weeks), upon which it crawls up its mother's belly and attaches itself to a nipple (which is located inside the pouch). It remains attached to the nipple for a number of weeks. The offspring later passes through a stage where it temporarily leaves the pouch, returning for warmth and nourishment.
-also because for fishes and other aquatic animals can simply release the sperm and egg cells directly into the water, because the sperm cells can swim on their own. amphibians such as frogs can also return to water to mate..
-however, vertebrate animals such as birds, mammals, and reptiles, etc. cannot go to the water to mate so the male must place the sperm cells directly into the females body.
2007-04-23 16:50:41 · answer #3 · answered by anshika g 1 · 0⤊ 0⤋
Their eggs don't leave the body until fertilized and by then they have a protective covering.
2007-04-23 16:00:48 · answer #4 · answered by bravozulu 7 · 0⤊ 0⤋