Ovaries

Like all mammals, the queen has two ovaries (1). The ovaries are suspended by several key ligaments, the ovaries are located caudal to kidneys and found inside a small peritoneal cavity called the ovarian bursa, which contains the ovaries and oviductal infundibulum, facilitating the transfer of oocytes into the oviduct (2). The ovaries are encased by a connective tissue layer called the tunica albuginea. Over this layer lies a simple squamous mesothelium, termed the germinal epithelium. Within the ovary is a cortex that houses the ovarian follicles and a medulla rich in blood vessels (3). Ovarian follicles are crucial structures within the ovary, responsible for oocyte growth, maturation, and release during the reproductive cycle. Each follicle houses an oocyte and goes through multiple stages of development leading up to ovulation (6). 

Oviducts

The oviducts of the queen are typically 5-9 cm long and are responsible for the transport of the oocyte to the uterus. The oviducts are made up of four parts (proximal to distal): fimbria, infundibulum, ampulla, and isthmus (3). Fertilization occurs at the junction of the ampulla and the isthmus. The ciliated simple columnar epithelium lines the oviducts, helping to propel the oocyte towards the uterus, while the surrounding muscularis externa assists in moving the fertilized egg, or zygote, into the uterine cavity for implantation (4). 

Uterus and Cervix

The queen has a bicornate uterus, characterized by a short body (~2cm) and two uterine horns (7-10 cm) (1). The bicornate structure of the cat's uterus is advantageous for multiple gestations as each horn can house several embryos, simultaneously allowing for multiple kittens (11). The tract of the uterus is lined by simple columnar epithelium and lies overtop of the endometrium. The endometrium is made up of the stratum functionalis and the stratum basale (4). The secretions of the uterine or endometrial glands in the endometrium provide nutritional support to the conceptus and may assist in adhesion to the uterine wall (5). A smooth muscular layer called the myometrium surrounds the endometrium (3). The cervix of the queen is located at the caudal end of the uterine body and consists of a thickened muscular area. 

Vagina

The vagina is a muscular tube comprised of the mucosa, muscularis, and the adventitial layer. The mucosa, which lines the lumen of the vagina, is made up of the epithelium (squamous stratified) and the lamina propria (dense non-glandular connective tissue). The muscularis has an inner circular and outer longitudinal layer of smooth muscle. The adventitial layer surrounds the vagina and connects to the bladder and rectum (3).

Penis

The penis of the male cat is located ventrally to the testicles. Penile spines cover the glans penis of the postpubertal tom due to the increase in androgens associated with puberty. However, after castration, penile spines regress within two months (7). The penile spines comprise keratinized epithelium and contain mechanoreceptors, which may play a role in pelvic thrusting behavior (8).

Testicles and Scrotum

The testicles of the tom are located within the scrotum. The scrotum is a dual-chambered skin sac containing the testes, epididymis, ductus deferens, and blood vessels (7). The inside of the teste is filled with seminiferous tubules. The epithelium of these tubules is made up of Sertoli cells, which support and regulate the developing spermatogenic cells also found in the epithelium. Leydig cells surround the tubules and secrete androgens. The center area of the testicle is made up of the rete testes, or collecting ducts, that transport spermatozoa to the epididymis (9). A layer of epithelial tissue surrounds each testicle, termed the tunica albuginea (9). 

Epididymis, Ductus Deferens, Vas Deferens

The epididymis is the location of sperm maturation. It is made up of the caput (head), corpus (body), and cauda (tail) (7). Efferent tubules transport the spermatozoa from the rete testes to the epididymis. In the tom, the cauda is located on the dorso-caudal portion of the testicle and becomes the ductus deferens. The ductus deferens leads cranially to the vas deferens, which enters the prostate gland (10). 

Prostate and Bulbourethral glands

The prostate gland of the tom is located ~2-3 cm caudal to the bladder and comprises four lobes surrounding the urethra dorsally and laterally (7). The epithelium of the prostate is made up of two layers: a secretory cell layer and a basal cell layer (10). The secretory epithelium's secretions make up the majority of the ejaculated seminal fluid (7). The secretory epithelium is also androgen-dependent and thus atrophies after castration (10). The two bulbourethral glands found in the tom are located bilaterally to the urethra, approximately at the base of the penis, and are 4-5 mm in diameter (7). 

Image Source: Illustrations have been modified from Merk Veterinary Manual