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前年,我讲三年级第二册自然16课《青蛙和蟾蜍》一课时,按教材笼统地讲了青蛙、蟾蜍的发育史。备课查阅参考资料时,我发现了一个问题,青蛙、蟾蜍从蝌蚪发育成蛙,它们的后肢同时长出,对于前肢的生长情况没有介绍。那么,它们的前肢是不是同时长出来呢?带着这个问题,我和生物组的同学捞了一些块状青蛙卵进行观察。 蛙卵(不知何时产的卵)捞到后2天孵出了幼蝌蚪。幼蝌蚪是极小的鱼形,没有
Two years ago, I said the second grade of the third grade of natural 16 classes “frog and toad” a class, according to the textbook general told the frog, toad developmental history. When preparing lessons for reference, I found a problem. Frogs, toads developed from tadpoles to frogs, and their hindlimbs grew at the same time. There was no introduction to the growth of forelimbs. So, their forelimb is not also out at the same time? With this problem, I and some students in biology group fishing lumps of frog eggs for observation. Frog eggs (I do not know when the eggs produced) 2 days after fishing hatched young tadpoles. Young tadpoles are tiny fish, no