118 



G. F. MATTHEW: ILLUSTKATIONS OK 



tubercles may be seen at this stage, arching around the inner slope of the chBok, and other 

 rows around the outer edge ; the outer rows are not perfectly regular and continuous, as 

 other rows run into them from the upper slopes of the cheek. 



Shield 8 X 15J mm. {Fig 33.) — At this stage, in the examples I have, the tubercles 

 on the cheeks do not show so regular an arrangement as in smaller tests ; but those of the 

 glabella continue to exhibit great regularity, as described of the adult on a previous page. 

 In this size the general aspect of the shield is more like the adult than it is in the smaller 

 tests. All the furrows are now present and are deeply impressed ; the central, trian- 

 gular part of the anterior marginal fold is wide and decidedly elevated. The posterior mar- 

 ginal fold, however, continues narrow and sharp. The ocular ridge now presents num- 

 erous branches spreading toward the anterior margin. 



Shield 19 x 38 mm. — At this, which is near the adult stage, the mature form, except 

 in the matter of width, is nearly or quite attained, the tubercles are more irregularly 

 scattered over the surface of the test, and the posterior margin is strengthened. 



Shield 20 X 4G mm. — This, the adult form, exhibits the completed exj^ansiou of the 

 shield laterally. The simplicity in the arrangement of the tubercles, so well seen at the 

 8 X 15|- stage, is here apparently lost, but, on carf^ful examination, traces of it can still be 

 detected in the apparently confused grouping of raised points on the surface of the 

 glabella. And the same may be said of the tubercles on the cheeks, which along the front 

 still exhibit a rude parallelism. To the heavier tubercles along the back, or higher xjart 

 of the anterior marginal fold, numbers of smaller tubercles are added in these later 

 stages, the whole being graded to quite small tubercles along the verge of the shield. 

 The additional tubercles scattered over the surface of the shield in the larger tests are 

 not always present, there being smooth individuals, which have no more tubercles than 

 those found on the smaller tests. 



The following table will show the changes in the proportions of the cephalic shield 

 and glabella of C. elegans during growth : — 



COMPARATIVE SIZE OF HEAD AND GLABELLA OF C. ELEGANS AT DIFFERENT AGES. 



