390 RIOHAED EVANS. 



Special Features of Type D. 



In this type of larva the same three kinds of cells take part 

 in the formation of the inner mass as in types B and C, but 

 the numerical proportion is very different. In types B and 

 C the individual elements of the cell groups are as numerous 

 as either the cells with granular nuclei or the cells with vesi- 

 cular nuclei ; but in type D the number of the cell groups is so 

 small that, had they not been discovered in the other types, 

 they would most probably have been overlooked. However, 

 they seem to be present always, though the groups often 

 consist of only four or five cells, and are few in number 

 (fig. 6a,g.c.). 



The cells with granular nuclei occupy the same position as 

 in type C, and present individually the same characters. A 

 noticeable feature in connection with them in both larvse is 

 their irregularity of form when they are examined from the 

 flattened surface. In consequence of this, the so-called mem- 

 branes, one of which lies under the flagellated layer and the 

 other lines the larval cavity, are far from being complete even 

 when they are best developed (fig. 10). Another feature, 

 equally noticeable with the above, is that the cells with 

 granular nuclei situated in the solid part of the inner mass 

 scarcely ever flatten out to surround lacunar spaces or canals, 

 which are almost completely absent from this larva. Their 

 nucleus varies considerably in both shape and size, measuring 

 from 3 to 4^- fi across, but remains uniform in structure, 

 whatever their position. The chromatin granules are always 

 small in size, irregular in shape, and situated at the nodes of a 

 nuclear reticulum which consists of fine threads enclosing 

 small meshes. 



The '' cell groups " are few, and consist of a small number 

 of cells, as has been mentioned above. Their individual 

 elements average about 5 ^ in diameter, and the nucleus varies 

 from If to 2^ /i in diauicter, a size which agrees closely with 



