Sentence:  The excretory vessels form a hairpin loop just inside the <WSD>phyllidium</WSD> (Pl. 5 Fg.1). It seems strange that the excretory vessels do not extend to the margins of these giant <WSD>phyllidia</WSD> since they invariably do in other forms with large <WSD>phyllidia</WSD> such as "Phyllobothrium lactuca", etc. 
Meaning of the word marked with <WSD> tags:  A muscular, leaf-shaped or cuplike outgrowth from the lateral wall of the scolex of some cestodes.