Sentence:  For example , the marked susceptibility of the monkey to respiratory infection might be related to its delicate , long alveolar ducts and short , large bronchioles situated within a <WSD>parenchyma</WSD> entirely lacking in protective supportive tissue barriers such as those found in types 1 , and 3 , . 
Meaning of the word marked with <WSD> tags:  animal tissue that constitutes the essential part of an organ as contrasted with e.g. connective tissue and blood vessels