Eisig, "Die Capitelliden," Fauna u. Flora G. v. Neapel, Monogr. xvi. 1887, p. 331.
Compare with this the muscular organ of Dinophilus, p. [243], Protodrilus, and a similar structure which occurs in Terebellids.
Korschelt, "Über Ophryotrocha puerilis," Zeitschr. f. wiss. Zool. lv. 1893, p. 224.
Eisig, Mt. Zool. Stat. Neapel, ii. 1881, p. 255.
They are specially large also in the Typhloscolecidae; while Racovitza (Ann. Mag. N. H. (ser. 6), xv. 1895, p. 279) has recently suggested that the caruncle of Amphinomidae belongs to the category of nuchal organs, and compares it with the ciliated lappets of Pterosyllis.