8 BULLETIN OF THE 



haare" seen by Iijima in other Triclads at the anterior margin midway 

 between the areas of the " Tastorgane " ; nor have I found in Phagocata 

 that the cilia in fhe head region move in different directions, as Minot 

 ('77, p. 407) has observed in the case of other fresh-water plananans. 



There has been a difference of opinion among writers as to the possi- 

 bility of certain regions of the body being normally destitute of cilia. 

 Metschnikow ('66, p. 436) and Kennel ('79, p. 125) found cilia covering 

 the whole surface in Rhynchodesmus and Geodesmus, but Zacharias 

 ('88, p. 542) states that the dorsal surface of a variety of Geodesmus is 

 bare, and Vejdovsky ('90. p. 132) maintains the same for Microplana, 

 the cilia in the latter cases being confined to the ventral surface or sole. 

 It seems to me, however, that Moseley ('74, p. 118) long ago offered a 

 satisfactory explanation of the condition, by saying that in Bipalium the 

 cilia on the dorsal surface of land planarians, being weaker through com- 

 parative lack of function, are consequently more easily destroyed by the 

 action of the reagents used in the preparation of the material. Consid- 

 ering the habits of land planarians, and especially the dissimilar condi- 

 tions to which the dorsal and ventral surfaces are subjected in regard to 

 moisture, exposure, contact, etc., it is not strange that the conditions 

 of the cilia of the different surfaces should be unlike. Iijima ('84, 

 p. 366) states that it is the exception for the edges of Dendrocoelum lac- 

 teum to be ciliated, and that the almost constant absence of cilia is due 

 to certain parasites (Trichodina). He also speaks of a species of Geo- 

 plana from South America in which the cilia of the dorsum are replaced 

 by a granular crust. I believe that in planarians there is primarily 

 no localization of the cilia, and that all non-ciliate conditions are 

 secondary. 



I could nowhere find a cuticula. The superficial portion of the cells 

 of the hypodermis takes a somewhat deeper stain than the body of the 

 cells, but there is no sharp line of demarcation between the two; the 

 color of the superficial portion fades gradually into that of the body of 

 the cell. A true cuticula such as that described by Minot (77, p. 407) 

 and Loman ('87, p. 69) for Triclads, and by Keferstein ('68, p. 16) for 

 Eurylepta, is wanting, and there is only a thickening, a condensation, 

 of the superficial plasma of the hypodermal cells. 



The hypodermis has proved to be the most difficult of the tissues to 

 study, because of the minuteness of its elements, and the enormous 

 number of dermal rods, or rhabditi, which so obscure the true condi- 

 tions that it is only after long and patient study of thin sections and of 



