METAZOA ARACHNOZOA. 365 



before hatching (fig. i) shows the anterior region (which 

 in this case is the cephalothorax) and the three-lobed 

 abdomen. The anterior segments of the abdomen at this 

 stage are separate, and the posterior part has segments 

 that are distinctly seen. The ventral view of the same 

 embryo (fig. 2) exhibits the six pairs of appendages 

 attached to the cephalothorax (also seen in fig. 3, side 

 view) and two pairs of leaf-like organs to the abdomen 



(fig. <o- 



The adult Limulus (No. 900. A, dorsal side ; B, ventral 

 side) is protected by a chitinous exoskeleton, the parts of 

 which have been separated in the preparation (C). The 

 cephalothoracic region is horseshoe-shaped, while the 

 abdomen lies behind and extends backward into a long, 

 sharp, movable spine. A flexible membrane at the junc- 

 tion of the cephalothorax with the abdomen enables the 

 animal to bend its body. Traces of segmentation are seen 

 on the dorsal side of the cephalothorax (No. 900, A) and 

 more plainly on the abdomen, where seven segments can 

 be ma'de out in part. The consolidated portion behind 

 these segments "7s supposed to consist of five segments 

 soldered together so that even their sutures are lost. 



Limulus has a pair of single eyes situated one on 

 either side of the anterior median spine. The compound 

 eyes are aggregations of single eyes and quite different 

 from the more specialized compound eyes of Crustacea 

 and insects. They are situated far back on the cephalo- 

 thorax and are widely separated. 



The cephalothorax bears six pairs of appendages and 

 the short metistoma or under lip situated back of the 

 mouth (No. 900, C). The first pair of appendages are 

 in front of the mouth and bend backward over the open- 

 ing. The succeeding five pairs are adapted for walking 

 and seizing food. All excepting the sixth pair, which is 

 used in pushing and in propping up the body, terminate 

 in a claw, and their inner section carries a leaf-like part 

 thickly covered with hair. 



