The stomach has three types of contractions: There are rhythmic, 3 per minute, synchronized contractions in the lower part of the stomach, which create waves of food particles and juice which splash against a closed sphincter muscle (the pyloric sphincter) to grind the food into small particles.
7 What is the gestation period, how many babies do they have, and when are they weaned? 1  The gestation period for rats is 19â22 days, for mice it is 17â21 days.  Rats and mice average 8â12 babies in a litter, but can have as few as 1 or as many as 20.
Tom Brakefield/Stockbyte/Getty Images. Porcupine babies are born more developed than the babies of many other types of rodents, mostly because porcupines tend to have one baby at a time instead of litters, and they carry the babies for up to seven months before delivery. But the babies still need their moms, and they sometimes stay with them for up to a year.