1902.] NATURAL SCIENCES OF PHILADELPHIA. 299 



the cells as iu the anterior (fig. 21), and the cells do not project so 

 far into the ccelorae as iu the median portion. The intercellular 

 fibres consequently are again shorter than the cell axis. 



Inside the cells, as has often been described, occur other fibres 

 taking the same course from the intima to the basement membrane. 

 Their disposition is varied, sometimes in bundles, as in fig. 4, or 

 singly, as in fig. 9. Again they may be strong throughout their 

 length, as iu fig. 4 (usually so iu the typhlosole), or may thin out 

 at one end, as iu fig. 9. In sections they cannot often be followed 

 continuously from intima to basement membrane because their course 

 is not often straight. They are more frequently straight iu the 

 typhlosole where they are thicker than elsewhere (figs. 3 and 4). 

 Where the fibres approach the intima or basement membrane they 

 are parallel and nearly always straight. This gives the so-called 

 ' ' striated ' ' border which has so often been described for the ' ' mid- 

 gut " of isopods (Lereboullet, Leydig (16), Huet, Ide, McMurrich, 

 Conklin, Schonichen). The great regularity of the fibres along the 

 intima is due to a thickening of them for a short distance in, thereby 

 producing what Schonichen calls the ' ' Balkchenzone. ' ' Both Mc- 

 ]\Iurrich and Schonichen regard this thickening as due to a deposition 

 of chitin on the fibres, basing their conclusion on a refractive index 

 in the fresh condition, and on a staining reaction in the preserved 

 material, similar to that of the inner border of the intima. Practi- 

 cally all authors agree that the thickened ends are continuous with 

 the intra-cellular fibres. I shall designate this zone of thickened fibres 

 by the term palisade, by which I would emphasize merely the parallel 

 arrangement of the fibres at their ends. Very often the spaces 

 between the thickened ends are empty of cytoplasm, which of 

 course strengthens the impression of a separate zone. This zone 

 does not have definite limits, as can be seen in starved cells, where 

 it may extend into the cell as far as the nucleus. In such a case 

 the only difference discernible in the course of the fibres is <hat they 

 are slightly thicker at the luminal end. Again, as may be seen in 

 figs. 9 and 11, the cyioplasm fills the intervals between the fibres all 

 the way to the intima. Thus the width of the zone may vary from 

 7iil to more than half the thickness of the cell, according, as we 

 shall see, to the physiological condition of the cell. 



McMurrich speaks of the brittleuess of the fibres, inferring this 

 property from their cleavage in sections. Conklin calls attention 



