in size 本来是什么意思？

The Dog And The Shadow 狗和它的影子
A DOG, crossing a bridge over a stream with a piece of flesh in his mouth, saw his own shadow in the water, and took it for that of another Dog, with a piece of meat double his own in size. He therefore let go his own, and fiercely attacked the other Dog, to get his larger piece from him. He thus lost both: that which he grasped at in the water, because it was a shadow; and his own, because the stream swept it away.
一条狗嘴里叼块肉,来到一座桥上.它看见水里有自己的影子, 以为是另一条嘴里也叼着一块比自己那块肉大一倍的狗.它忙丢下自己嘴里的那块肉,猛力地攻击水里的狗.试图去抢它的肉.结果,它两块肉都得不到. 因为那只是一个影子,它自己的影子而已.真正的肉也被水冲走了

这片短文中 with a piece of meat double his own in size这句是什么意思？
里面的in size 是什么意思 还有double his own什么意思？
高手帮帮忙 感激不尽……

这片短文中 with a piece of meat double his own in size这句是什么意思？
里面的in size 是什么意思 还有double his own什么意思？

with a piece of meat double his own in size
叼着一块肉比自己那块大一倍

in size 指(肉)尺寸的大小

double (一倍)
his own(它自己的那块肉)

double his own 比自己的那块肉大一倍