MUSEUM OF COMPARATIVE ZOOLOGY. 15 



he says, " On treatment with potash, the cells of Bipalium swell up, are 

 seen to contain rod-like bodies, and the fine filament at the upper 

 extremity appears like a duct leading to the surface of the basement 

 membrane." 



Hallez.and Iijima do not make mention of any processes of the sub- 

 hvpodermal parent cells, but believe that the cells are ruptured, and that 

 the rhabditi make their way to the epidermis through the tissues of the 

 body. Hallez ('79, p. 6) says : " Jai ete temoin une seule fois de la rup- 

 ture d'une cellule productrice chez Mesostomum tetragon u rn ; il m'a ete 

 impossible de retrouver dans cette cellule rompue la moindre trace du 

 noyau." Iijima ('84, p. 371) writes as follows: "Die Bildungszellen 

 sind rundlich und mit einem ausserordentlich feinkornigen Inhalt ver- 

 sehen." And again : " Haben die Rhabditen ihre definitive Grbsse er- 

 reicht, so durchbrechen sie die Zellenwand, w T elche schlieslich absorbirt 

 zu werden scheint und wandern durch den Bindgewebe und die Basal- 

 membran entweder einzeln oder in Gruppen nach aussen in die Epidermis- 

 zellen, in denen sie definitiv verbleiben." 



Not all of the rhabditi that are developed in the parent cells of the 

 sub-hypodermal tissue find their way to the exterior. Many of the cells 

 apparently lose their connection with the hypodermis, and their rhab- 

 diti are discharged into the body parenchyma; only on this assumption 

 can one explain the presence of the numerous rhabditi that are found 

 scattered in the sub-hypodermal tissues. This condition is not the 

 normal, or at least not the original one. These often occur in large 

 numbers in the zone immediately inside of the longitudinal muscle 

 bands, which is occupied by the mother cells, where they lie in no 

 definite positions, and with their axes directed at all angles. 



Rhabditi of all sizes may be developed in the same parent cell. 

 Those of different sizes are not confined to special cells, as found by 

 Schneider ('73, p. 83) and Graff ('74, p. 128) for Mesostomum. Be- 

 sides the fully developed rhobditi there are in the cells particles that 

 have no constant form, but have the same optical appearance and stain 

 the same as the rhabditi (Figs. 6, 10). These bodies may be either 

 residual matter, disintegrating rhabditi, or incipient rods. They never 

 occur in the epidermis, but are left behind after the discharge of the 

 rhabditi, and by the absorption of the wall of the parent cell they fine 

 their way into the body parenchyma, where, with the rods previously 

 referred to, they lie scattered about. Lang ('84, p. 52) found similar 

 bodies along with the rhabditi in Polyclads, and speaks of them a: 

 " junge kugelige Stabchen." I am inclined to regard them as residua 

 secretions. 



