Spiders are easy to study since they don't fly away! This image shows the pedipalp of a male woodlouse spider (Dysdera crocata). Pedipalps are secondary reproductive organs. Observing the pedipalp can be a useful clue for identification of the species.
This pedipalp was cleared with clove oil. View a similar treatment of the mouthparts of a spider.
Find out more about spider's anatomy in the article 'what we can discover on a spider's leg'