ox THE DEVELOPMENT OF LIMULUS LOXGISPIXA. 6Î) 



appendage-ljearing segment is ^epai-ated from the cephalic lobe. After 

 two or three segments are cut off. the me-ohlast of tlie ventral plate is 

 divided in the median line into îwo lateral hah es, bei>inninii' from the 

 anterior end. in early .■stages the dafk Hues in the ventral [)late. 

 where few ov \io me.-ohlast cells are found, show froni the exteri<jr the 

 divifîion of the mesohlast into transverse segments as well as into two 

 lateral liah es (figs. 4-7). 



The mesohlast "which was separated into lateral moieties unites 

 again i'vnm the a.nterior end of the ventral plate. Afterwards there 

 is found a special compact accumulation of mesohlast cells in the 

 median line of the ce})halothorax above the nervous system (tigs. 51, 

 Ô2, 5t), t)8, cntosL). This accumulation is laterally very thick. It is 

 the rudiment ()f the entosternite. 



About tlu'ee weeks after fertilization, tlie mesoblastic dissepiments 

 are f)rmed in the cei)halothora.x bv the siidvinir in of mesohlast cells 

 into the yolk (ß'^^. 52, 57). They are intersomitic, dividing the yolk 

 into as many compa.rtments as there are segments. But there is no 

 dissepiments Ijetween the ce[)halic lobe and the first appendage-bearing 

 segment, aiid the dissepiment between tlie second and third ap])endage- 

 beariug segments arid that between the sixth and seventh appendage- 

 bearing segments are short. In the abdomen the dissepiments ure not 

 well developed. 



Céphalothorax and Abdomen. 



The céphalothorax consists of the cephalic lobe and tlie succeeding 

 seven segments. Tt firms the greater part of the cg^^, and becomes 

 gradually flat by the horizontal increase of the ventral plate. 



The deNelo]>meiit of" the a.lidomen takes place wvy late. At about 

 hie lime wlieii I he I \\ n nie. nbltir-tie plates of tlie seventh a pi ;eudage- 



