Sentence:  For example , the marked susceptibility of the monkey to respiratory infection might be related to its delicate , long alveolar <WSD>ducts</WSD> and short , large bronchioles situated within a parenchyma entirely lacking in protective supportive tissue barriers such as those found in types 1 , and 3 , . 
Meaning of the word marked with <WSD> tags:  a bodily passage or tube lined with epithelial cells and conveying a secretion or other substance