106 r. H. STEWART. 



an outgrowth of protoplasm from the cells of the longitudinal 

 lines and contains no nuclei. The longitudinal Hues are, 

 in fact, situations where the epidermal nuclei are aggre- 

 gated, and where the nutrition and general government of the 

 entire epidermis is carried on. 



I have described the lines as cellular, but although cell- 

 walls do occur, they are often not complete, the protoplasm of 

 one cell being at one point continuous with that of another, 

 or several nuclei may appear in one mass of protoplasm, and 

 as no cell-walls are to be found in the subcuticula, all the 

 cells whose protoplasm is continuous therewith are presumably 

 in this way continuous with one another, although this layer 

 is so thin tliat divisions might exist in it but be undemon- 

 strable. 



The four longitudinal lines lie, as usual, one mid-dorsal, 

 one mid-ventral, and two lateral, dividing a transverse section 

 of the body-wall into four quadrants. They extend, as I 

 have stated, from one end of the body to the other. Their 

 absolute and relative breadth varies in the different regions. 

 In the oesophageal regions all four lines are of fairly equal 

 breadth, and occupy each about one fourteenth of the cir- 

 cumference, each showing about four cells in transverse 

 section. 



In the intestinal region (PL 8, fig. 24) the median lines 

 decrease in size, showing only one or two cells in section ; the 

 lateral lines, on the other hand, ai-e considerably broader and 

 occupy each about one eighth of the circumference. Opposite 

 the gonads the lines are very much flattened from pressure. 

 Behind the anus they are of approximately equal breadth, 

 and each occupies one eighth of the circumference. 



Two types of cells occur — viz. (1) cells whose shape varies 

 from square to oval, and whose greatest diameter varies from 

 0-008G to 0"0107 mm. The protoplasm is fairly abundant and 

 is non-granular. The nucleus, spherical or oval, measures 

 from 0'0043 to 0"00538 mm., and has a well-marked nuclear 

 membrane containing numerous minute chromatin granules 

 and a nucleolus (PI. 7, fig. 9). (2) Rather smaller cells. 



