MUSEUM OF COMPAEATR^E ZOOLOGY. 19 



Yon Ihering ('80, p. 149) states that in the case of Graffilla murici- 

 cola, from the kidneys of Murex, concretions and rhabditi are altogether 

 wanting in the epidermis. Their function, he says, is one of protection, 

 and hence they are not needed in a parasite. Lang ('80, p. 108) says of 

 Graffilla tethydicola, from the foot of Tethys, that there are no rhabditi, 

 but " Unmittelbar unter den Haut liegt eine grosse Anzahl eizelliger, 

 bimfbrmiger, sich hauptsachUch mit Picrocarraine intensiv farbender 

 Driisen." Graff ('82, p. 375) says, concerning the same species, " Ueber- 

 dies finden sich hier unter der Haut zahlreiche einzellige birnfdrmige Drii- 

 sen." Anoplodium parasitica, a parasite in the body cavity of Holothuria 

 tubulosa, also possesses no rhabditi : " Ich habe weder an frischen noch an 

 conservirten Exemplareu von stdhchenformigen Korpern oder von irgeud 

 einem Pigmente etwas wahrnehmen konnen." (Graff, '82, p. 376.) 



In Planaria limuli, a Triclad ectoparasitic on Limulus polyphemus, I 

 have been unable to find any trace of rhabditi, but have found in 

 abundance sub-hypodermal glands that resemble the parent cells of 

 rhabditi, and like them send long ducts to the epidermis. Graff ('79, 

 p. 203) states regarding this species that there are no true rhabditi ; 

 but he speaks of certain " Haftorgane," which he compai'es to rosettes 

 of rod-like bodies, and then adds: "Die dieselben zusammensetzenden 

 Stabchen (Haftstabchen) bilden sich im Innern des Korpers in besou- 

 deren Driisen und farben sich ausserst intensiv in Carmine und Hama- 

 toxylin," — but I could not find these organs. 



Thus we see that in parasitic Turbellarians there are no rhabditi, 

 their place being taken by many sub-hypodermal glands. Assuming 

 that the rhabditi are condensed secretions used in securing prey and 

 for protection, the conditions present in parasitic forms are in every 

 way consistent with our conclusions. The only other possible function 

 for the rhabditi is that assumed by Graff ('82, p. 58) and stated by him 

 as follows : " Die plausibelste Anschauung ist auch heute noch die von 

 Schultze gegebene und von Stein auch fiir die Stabchen der Infusorien 

 adoptirte, wonach die Stabchen indem sie dem aussem Drucke einen 

 Widerstand entgegensetzen, in ahnlicher Weise befordernd auf der 

 feinere Tastgefuhl der Haut einwirken, wie der Nagel auf Tastver- 

 mogen der Fingerspitze." I have shown that on account of their inter- 

 cellular position the rods probably cannot have such a function ; but 

 even if this evidence were considered insufficient to disprove their sup- 

 posed office, one would have to encounter the objection that so important 

 a function would not be likely to be entirely lost in parasites, particu- 

 larly in such active ectoparasites as P. limuli, where the parasitism is of 



