The data file Maculatum.dat at the text website is from a study13 of salamander embryo development. These data refer to the spotted salamander

(Ambystoma maculatum). One purpose of the study was to compare four rearing environments (very humid air, and water with low, medium, and saturated dissolved oxygen) on the age at hatching, for each of the embryos that survived to hatching. In the experiment, embryos from the same family were divided into four groups for the four treatments, and each group was reared together in the same jar. For the embryos that survived to hatching, use multilevel modeling to compare the mean ages for the four treatments. Compare estimates and SE values to ones you would obtain with an ordinary linear model with treatment as the explanatory variable, ignoring the dependence due to embryos in the same jar being from the same family and due to the same family of embryos being in four jars.