The erectile organs (penis and clitoris) develop from the same anatomy in the foetus called the genital tubercle. The penis and clitoris have crura alongside the corpora cavernosa that cause tumescence. [i] It is inconceivable that the organ responsible for male orgasm would not be the same organ that is responsible for female orgasm. Some sexologists suggest that intercourse, which stimulates the vagina, can have a secondary effect on the clitoris because the two organs are adjacent to each other or because parts of these two organs are connected. This is like saying that men should stimulate the testes because they are adjacent and connected to the penis.
Kinsey noted that after adolescence, men need specific penile stimulation to achieve orgasm. Whether men engage in intercourse, masturbation or oral sex (fellatio), the penis is always involved. Equally, stimulation involves massaging the shaft of the penis that contains the corpora cavernosa. These structures trap blood and cause an erection. Being erect is what makes the penis so erotically sensitive (in a pleasurable way). The clitoris is an internal organ that is only ever tumescent (not rigid like the penis).
Confusingly when people refer to the clitoris, they usually mean the clitoral glans, which is the only externally visible part of the clitoral organ. Consequently many people assume that women should orgasm from stimulation of the glans. But if we look at the parallel for men, they do not typically achieve orgasm by stimulating the glans of the penis. Masturbation involves pulling the outer layer of skin up and down the shaft of the penis. This stimulation of the shaft by the hand provides more specific and effective stimulation than that provided by penetrative sex. The effectiveness of penetrative sex relies on the psychological turn-on for the penetrating male of thrusting his erect penis into another person’s body orifice.
When I compare my masturbation technique to a man’s, there are obvious parallels. I start by focusing on a fantasy to generate the arousal that I know from experience is vital to achieving orgasm. Without this mental response, stimulation is ineffective. The concept of penetrative sex as an erotic act (also of violation) is key to my ability to become aroused. Unlike a man, this mental process is conscious and never occurs spontaneously. I use the fingers of both hands to push down over the clitoral glans using a rhythmic technique (much slower than a man’s). Once aroused, I press down further either side of the labia, where the internal clitoral organ (containing the corpora cavernosa) is located, near the entrance to the vagina. This stimulation technique is incompatible with sociable sexual activity.
[i] The penis, for example, has two roots known as crura which play an essential role in its functioning. During sexual excitation these crura become engorged with blood and contribute to erection of the penis. The clitoris, too, has two broad roots, of approximately the same size as in the male. The clitoral crura, too, become engorged with blood early in the woman’s sexual excitation. (Shere Hite)
Excerpt from Understanding Sexual Response (ISBN 978-0956-894762)