MUSEUM OF COMPARATIVE ZOOLOGY. 17 



charged from the hypodermis, wh}'^ are they being continually devel- 

 oped throughout the lifetime of the individual? Something must be- 

 come of them, or there would be an accumulation too great to find 

 room in the hypodermis. 



Kennel ('88, p. 474) says, relative to this subject : " Lasst man sie 

 [planarians] aber in Uhrschalchen mit Wasser langere Zeit nnbehelligt, 

 so dass sie sich festsetzeu, und stort sie dann plutzlich, so ziehen sie sich 

 stark zusammen, machen heftige Bewegungeu und suchea zu entflieheu. 

 An der betr. Stelle aber findet man bei schneller Untersuchung Massen 

 von Rhabditen in alien Stadien der Auflosung, und weun man das Wasser 

 schnell ausgiesst, findet man dort ein Kliimpchen zahen Schleim, — die 

 Stabchen losen sich in Schleim auf." I have often repeated the experi- 

 ment of Kennel, and have always found rhabditi in large numbers in 

 the slime secreted by the worm when placed on a glass plate. 



We may now consider the question of the morphological and physiologi- 

 cal meaning of the rhabditi. Two interpretations of the morphological 

 value of the dermal rods have been given by naturalists. The larger 

 number of observers consider them homologous with the nematocysts ^ of 

 Coelentei-ates ; whereas the more recent investigators believe them to be 

 the morphological eqiHvalents of gland secretions. I coincide with the 

 latter explanation, and offer the following arguments in its support. The 

 parent cells are unicellular glands, and the rhabditi, their secretions, 

 like the secretions of other dermal glands, are voided from the body of 

 the individual. The rods cannot function as organs of touch in lending 

 resistance to the epidermis, as suggested by Max Schultze and main- 

 tained by many others, for they do not -lie in the epidermis cells, but 

 between them. The insensible gradations that exist between rhabditi 

 and the secretions of glands, as exemplified in the so called " Pseudo- 

 rhabditen," " Schleimstabchen," " Schleimblockchen," and " Korner- 

 drusen," have been to me one of the most striking evidences of the 

 glandular significance of the rhabditi. The dermal rods of Phagocata, 

 when acted on by reagents, present conditions resembling all the varie- 

 ties of dermal bodies figured by Lang, and, as T have said elsewhere, I 

 believe that the epidermal " gland-cells " of Moseley were only rhabditi 

 modified by acids. Sub-hypodermal glands and the mother cells of the 

 rods never occur together. Where rhabditi are absent, their place is 

 taken by glands, and vice versa. This is illustrated in the region of the 



1 According to Camillo Schneider ('90, p 375) even the nematocysts are to be 

 considered only as highly specialized secretory cells derived from simple gland 

 cells. 



VOL XXI. — NO 1. 2 



