Sentence:  The <WSD>radioles</WSD> of the second size are about 8 millims. in length and 2 millims. in width, very much compressed and flattened, rounded at the end and finely striated longitudinally. They are articulated in a single row to the small tubercles round the edge of the areola, and in their natural attitude they lean over the naked part of the areola and cover the muscles and the head of the large <WSD>radiole</WSD> like a frill. 
Meaning of the word marked with <WSD> tags:  The spine of a sea urchin. (from late 19th c.)