sisäkkäisen

Could you please clarify what "sisäkkäisen" refers to? I’m not sure whether it’s a Finnish term, a proper noun (person, place, or organization), a concept in a specific field, or the title of a work. If you can provide a bit more context (for example, whether it’s a linguistic term, a biological term, a place, or something else), I can write a concise, neutral wiki-style article (under 300 words) accordingly.