Botryllus schlosseri , a colonial tunicate , is a protogynous hermaphrodite. After the fall in circulating placental steroid levels, especially estrogens, during the first few days after birth, serum FSH and LH levels increase and exhibit a pulsatile pattern with wide perturbations for several months. There is a striking sexual dimorphism in the circulating concentration of leptin at birth, at which time females have higher levels than males, and again in late puberty and adulthood. Thus, testosterone leads to the development of the internal genitalia and dihydrotestosterone leads to the development of the external genitalia see Figures 3—1 , 3—2 , and 3—3. Some studies have used highly sensitive immunoassays to show that both prepubertal boys and prepubertal girls have a pulsatile pattern of serum LH and FSH concentrations, with higher concentrations during the night than during the day see Mitamura et al. The decreased leptin levels in late puberty in boys have been attributed to the action of testosterone Pubertal Growth Spurt One of the most striking sex differences in puberty is the earlier age of onset of the pubertal growth spurt and the earlier attainment of peak height velocity in girls, in contrast to the later onset of the increased rate of growth and greater peak height velocity in boys. In female development, proliferation of the vesicovaginal septum pushes the vaginal orifice posteriorally so that it acquires a separate external opening; thus, no urogenital sinus as such is preserved. For example, eggs are larger than sperm, thus if you are a big you are able to make more eggs so being female when big is advantageous, however the size advantage relationship is really not as simple as the example just mentioned, but it allows for a better understanding. Penile length in the male increases linearly at about 0. Clownfish have a very structured society. The onset of breast development in African-American girls is about 1 year earlier than that in Caucasian girls, even though the average age of menarche in a large cross-sectional study was different by only 0. The largest non-breeding fish then sexually matures and becomes the male of the group. It is the critical role of the testes in male duct development to provide high local concentrations of testosterone. In its case, functional protandry refers to the emergence of male adults 2—3 weeks before female adults.