454 W^ NICKERSON. 



a new species, Distomum calytrocoiyle, to contaiu vesicular structures 

 in the cuticula which he interi)rets as degenerate nuclei. This is 

 followed by a résumé of the evidence from other sources which seems 

 to him confirmatory of his views. 



Numerous small spherical or rounded globules, which stain dif- 

 ferently from the surrounding substance, are indeed present in the 

 outer layer of the body of Siichocotyle. There is however nothing 

 in their appearance to give any ground whatever for interpreting them 

 as nuclei or as remnants of nuclei. 



I believe that there is a method of explaining them which is 

 simpler and ujore natural and which will at the same time atl'ord a 

 satisfactory explanation of most of the other conditions present. I 

 shall return to a consideration of this later. 



There is yet another theory to account for the outer layer of the 

 body of Trematodes; it is unsupported by any considerable amount 

 of evidence, but nevertheless it seems to account for all the conditions 

 presented in a more satisfactory manner than either of the older 

 theories. I refer to that recently suggested by Looss ('93). This in 

 brief is as follows. The parenchyma of the body is formed from a 

 layer of undifferentiated cells lying just beneath the muscle layer and 

 compared by Looss to the cambium of plants. In the transformation 

 of these cells into the highly vacuolated condition of the character- 

 istic deeper lying parenchyma there is produced a large quantity of 

 formed material, which is set free in a region just beneath the outer 

 wall of the body. This makes its way through the musculature and 

 the outer layer to the exterior in small particles or globules, and here, 

 by confluence of the globules, becomes converted into the so-called cuti- 

 cula, later formed portions being added to the layer already present. 



Several facts seem to confirm this theory more than eitlier of 

 the others mentioned. There are frequently found scattered throughout 

 the thickness of the outer layer minute, more or less globular spots 

 which take stains less deeply than the general mass of the layer. 

 These are most frequently of even , circular outline and the greater 

 number of them are of small size — from 1 to 2 ^^ in diameter — though 

 the largest sometimes measure as much as 8,5 //. Occasionally 

 however they are irregular in outline and may also be elongated io 

 a direction perpendicular to the surface of the layer. They are present 

 in sections of tissue killed l)y various reagents and stained by dif- 

 ferent dyes. 1 am inclined to regard them as being due to the 

 presence in the outer layer of small globular masses of the recently 



