(a) Draw a well-labelled diagram of testis and ovary in mammals, and discuss the functions of their hormones. 20 (b) Give an…

Mammalian gonads and hormones. A labelled diagram of the testis would show a tunica albuginea enclosing coiled seminiferous tubules, where Sertoli cells support spermatogenesis and secrete androgen-binding protein and inhibin, while interstitial Leydig cells between tubules secrete testosterone. The ovary diagram would show primordial, primary, secondary and mature Graafian follicles in the cortex, a corpus luteum after ovulation, and stromal tissue with theca cells. Both are controlled by the hypothalamic–pituitary–gonadal axis: GnRH from the hypothalamus stimulates anterior pituitary FSH and LH. In males, FSH acts on Sertoli cells, LH on Leydig cells; testosterone maintains male secondary sex characters, supports spermatogenesis and libido, and feeds back negatively on the hypothalamus and pituitary, while inhibin specifically suppresses FSH. In females, LH stimulates theca cells to produce androgens, and FSH stimulates granulosa cells to aromatise those androgens into estrogens; after ovulation, the corpus luteum secretes progesterone. Estrogen and progesterone act on the uterus, mammary glands and secondary sex characters, and feed back on the HPG axis; in many species, rising estrogen gives positive feedback to trigger the LH surge. In many mammals, luteolysis by prostaglandin F2α ends the estrous cycle, while menstruation is restricted to primates and a few others. Relaxin, from the corpus luteum/placenta, relaxes the cervix and uterus and supports mammary development. Thus male and female systems are coordinated by the same axis but differ in cyclicity, target organs and luteal fate.

Reptilian skull types. An illustrated account would show three basic patterns of temporal fenestrae, which reduce skull weight and provide attachment areas for jaw muscles. Anapsids, typified by turtles, lack temporal openings, giving a solid skull with strong jaw muscles but limited jaw mobility. Synapsids, the mammal-like reptiles such as pelycosaurs and therapsids, have one lower temporal fenestra, allowing larger jaw muscles and more efficient feeding. Diapsids, including lepidosaurians and archosaurians, have two pairs of fenestrae: an upper temporal bounded by postfrontal, parietal, squamosal and postorbital bones, and a lower temporal bounded by postorbital, jugal, quadratojugal and squamosal. Evolutionarily, the anapsid condition is ancestral, synapsids modified the lower opening, and diapsids retained both openings; crocodilians retain both, while dinosaurs and birds reduce them. Later lineages show secondary modifications: snakes have elongated skulls with modified fenestrae and kinetic jaw elements for swallowing large prey, while birds, derived diapsids, have generally akinetic skulls with reduced fenestrae, a beak and limited exceptions such as rhynchokinesis.

Fish migration. Fish migration is classified by habitat change. Anadromous fishes live in the sea and enter rivers to spawn, e.g., salmon and Hilsa (Tenualosa ilisha) in the Ganga–Brahmaputra and Bay of Bengal. Catadromous fishes spawn in the sea, e.g., eels. Potamodromous fishes remain in freshwater but move within it, e.g., Indian major carps such as catla, rohu and mrigal migrating upstream in the Ganga, Brahmaputra and Godavari for spawning. Oceanodromous fishes migrate within marine waters, e.g., sardines (Sardinella) and mackerel (Rastrelliger) along the Indian coast. Photoperiod, temperature and salinity act as cues; the pituitary–thyroid axis and gonadal hormones regulate readiness, gametogenesis and movement. Navigation uses magnetic fields, olfactory imprints, water temperature, salinity and celestial cues. Ecologically, migration transfers nutrients, connects habitats and maintains population structure; economically, it determines seasonal landings, livelihoods and aquaculture seed collection. Management therefore needs river flow, closed seasons under Marine Fishing Regulation Acts and state laws, bycatch reduction and climate monitoring.

Together, these patterns show vertebrate adaptation: mammalian reproduction integrates structure and endocrine feedback, reptilian skulls illustrate fenestration and kinetic modification, and fish migration links physiology, navigation and fisheries. This integration is essential for understanding vertebrate diversity and sustainable use.