The cladogram of the kingdom animalia shows the relationship of selected animals based on their shared anatomical features. the black numbered squares represent features that are critical for forming each branch in the animal kingdom. square one represents a dorsal nerve cord, which means the animals in all the branches have a dorsal nerve cord.

which numbered square would represent the trait "mammary glands? "

hi~~

i would say that hybridization occurs frequently in nature, because there are many types of hybrids that have occurred naturally, such as the mule (male donkey + female horse)

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

i hope this : )