Section 155 of the Criminal Code prohibits the act of incest. The section reads as follows:

Everyone commits incest who, knowing that another person is by blood relationship with his or her parent, child, brother, sister, parent grandparent or grandchild, as the case may be, has sexual intercourse with that person.

Sexual intercourse is defined in section 4(5) of the Code; it states:

For the purposes of this Act, sexual intercourse is complete on penetration to even the slightest degree, notwithstanding that the seed is not emitted.

KH was charged with a number of sexual offences including incest all perpetrated against his underage sister. Numerous incidents were alleged which included forced fellatio and several acts of KH penetrating his sister’s anus.

At the close of the Crown’s case, KH brought an application for a directed verdict on the incest charge. KH argued the following:

The purpose of section 155 is to prevent “sexual intercourse between persons who have a blood relationship” in an effort to “prevent genetic mutations that can result from inbreeding” and to protect of vulnerable family members. [at paras 6-7]
The fact that section 4(5) includes the phrase “notwithstanding that seed is not emitted” indicates that what is contemplated is penetration of a vagina by a penis.
That Parliament also enacted (the now unconstitutional) section 159 prohibition against anal intercourse, further supports the defence position on the definition of sexual intercourse.

Barnes J dismissed the application: 2015 ONSC 7760 and held that:

The defence argument falls apart when considered in the context of the second legislative intent, which is the protection of vulnerable members of the family. A definition of sexual intercourse limited to penile penetration of the vagina means that a male can only commit incest if he uses his penis to penetrate the vagina of a blood relation. Under this circumstance, the "vulnerable family member" is only protected from incest if she is female and if the penis is inserted into her vagina. The same female blood relation is not protected from incest if her male blood relation inserts his penis into her anus.

Another consequence of restricting sexual intercourse to the penile penetration of the vagina is that a vulnerable family member cannot receive the protections provided by s. 155 of the Criminal Code simply because he is not female. On the defence theory, if a male places his penis in the anus of a vulnerable family member who is male, he cannot be charged with incest. The protection of vulnerable female family members to the exclusion of vulnerable male family members could not have been the intention of the legislature. [at paras 16-17]

Barnes J’s common sense approach to this issue is in accordance with the principles of statutory interpretation which the court reviewed prior to reaching its conclusions.