410 Wm. S. Marshall and C. T. Vorhies, 



plasm there necessarily goes a corresponding increase of the outer 

 layer. In this latter part a distinct striation is very noticeable, the 

 striae passing from the outer surface of the gland to near the inner 

 margin. These striations are perpendicular to the tunica propria and 

 run fairly straight until the median plane of the cell is reached; at 

 this point the striae curve, as previously noticed, toward the nearest 

 piece of the nucleus. There are also present in this outer region 

 small irregular vacuoles and small areas which are distinguished by 

 their darker coloration and greater density of the cytoplasm. These 

 areas are mostly near the outer margins of the cells. 



The changes in the nucleus are not great, the most noticeable 

 being the almost constant irregularity of the membrane along its outer 

 surface. The nuclear membrane on the side toward the lumen of the 

 gland is even, or, if not so, the irregularities are none of them sharp 

 or abrupt; the outline here follows quite regularly that of the gland. 

 The outer membrane, however, has a number of longer or shorter 

 pointed processes extending out into the cytoplasm. The nucléoles 

 show here a slightly greater irregularity in shape, some pieces being 

 very uneven in outline and bearing a number of fairly long projections. 

 A surface view of the nucleus shows a greater number of the nucléoles 

 to be elongated; in some sections we noticed two, three, or four 

 „macrosomes" which were end to end and had the appearance of having 

 been parts of a larger piece. 



Both the larvae taken after rebuilding their cases for a period 

 of one hundred and twenty hours must have been very active, as we 

 found in their glands a well marked change. The structure of both 

 cytoplasm and nucleus (Fig. 17) resembles here very closely what we 

 shall find in larvae which have supposedly done more secreting; those 

 which, at least, have been working for a longer time. In these glands 

 we find, along the inner portion of the cells, oìì\j a narrow area in 

 which the cytoplasm shows no change. We have already noticed that 

 this area in which the cytoplasm is of a similar structure throughout, 

 decreases as the period of activity increases, and we now find it 

 occupying but a narrow strip just along the inner membrane. In these 

 glands of one hundred and twenty hours activity it has in part lost 



