Sentence:  Having considered their animal nature, and their primary formation, as involving the question of spontaneous generation, he described generally the methods of reproduction adopted in this class of animals, ad adduced the explanations and opinions offered by the best authorities on the subject, but particularly those of Bremner, Lænnec, and Owen, by which acephalocystic reproduction is referred to imperfect <WSD>ovation</WSD> or generation. 
Meaning of the word marked with <WSD> tags:  The act or state of laying eggs.