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OTT. [Vol. VII. 



was fixed in corrosive sublimate and stained in Mayer's carmine. 

 He says that the bottom of each pit is covered with a thick layer 

 of homogeneous substance which may be regarded as mucus. 

 Below this is a thin layer of ciliated epithelial cells whose cilia 

 project through the homogeneous layer. Next to this is a much 

 thicker layer which is made up mostly of pyriform cells, although 

 there are other histological elements scattered through it. Next 

 to this layer is the ganglion which is connected with the nerve. 

 Landsberg bases this description upon a single series of sections. 

 As a result of a process of maceration he found in the pits : 

 I, bipolar and some multipolar ganglion cells the processes of 

 which form plexuses ; II, ciliated epithelial cells of various sizes ; 



III, partly membranous cells which have an investing function ; 



IV, goblet-like mucous cells ; V, a very regular network which 

 stands at right angles to the muscle fibres ; and, VI, special 

 sense cells. These last cells have one end drawn out into a 

 lone: fibre, and the other end formed into a brush-like mass of 

 fibres. 



I have tried the methods by which Landsberg obtained his 

 sections, but have been unable to confirm his statements. 



Sections of worms which were fixed in either corrosive sub- 

 limate or chrom-osmic-acetic acid, and which were stained in 

 either alum carmine, borax carmine, picro-carmine, or hasmatoxy- 

 lin show the wall of the ciliated pit to be made up of a single 

 layer of epithelial cells together with a muscular layer, both of 

 which are continuous with the corresponding structures in the 

 integument. These sections also show that the ciliated pits are 

 embedded in the anterior ends of the brain ganglia. The same 

 results are obtained in either longitudinal sections or cross-sec- 

 tions. Sagittal longitudinal sections through the brain lobes 

 show no break between the ganglion cells surrounding the pits 

 and those of the posterior end of the lobes which are connected 

 by the commissure. In serial cross-sections no break can be 

 seen from one section to another. I have seen no case of a 

 nerve passing to the ciliated pits. 



When the ciliated pits are developed, they are formed as 

 simple depressions of the integument. There are three possible 

 methods by which the two layers described by Landsberg 

 might be produced : i, by a division of the epithelial cells ; 2, by 

 a migration of cells from the brain ganglia to the walls of the 



