ox THE DEYELOPMEXT OF LIMULUS LOXGISPIXA. 61 



bearing segment had appeared (cf. fig. IS J. The ninth appendage had 

 been produced. The second, third, fourth, and fifth appendages had 

 become chelate. The rudiment of the flabeJlum was found as a small 

 round prominence on the outside of the sixth appendage. A siüiüar 

 ])rominence was also found in the segment of the fiftli appendage, 

 Tlie nervous system w'as seen as indistinct, wliite, longitudinal hands 

 near the median line. In the Ijrain, paired inva_oinati(Mis were f )und. 

 The marginal band had moved much farther outward, so that the 

 outei- h'tcral longitudinal groo\e had become very wide and shallow. 

 The first appendage was found at the level of the stomodteum. 



On August 18th (21 days after fertilization), mesoblastic dissepi- 

 ments were found, and the homodynamous organ to the flabellum was 

 seen in the segments of the fourth, third, and sec<jnd appendages 

 (fig. 13). 



From August 19th onwards, the abdomen became gradually pro- 

 minent by the development and addition of new segments. The 

 hatclied embryo has ten abdominal segments. Tliis number corres- 

 ponds to the number found in the adult animal. The sixth and the 

 first appendages became chelate. The seventh appendage gradually 

 degenerated from the distal end, and at last a small proxinud portion 

 only remained as tlie metastomum. As the ventral plate increased its 

 surface \ery rapidly, the at first spherical egg became fiat dorso- 

 ventrally, and the egg assumed the trilobite-like shape (fig. 17). 

 The lateral hunij) separated grtidually from the marginal ])and and 

 w^as found in the trilobite stage «ju the (bjrsal side of the eml)rvo. 



Internal Changes. 



A section cut through the wliite disc found in the embryo (fig. o) 

 of August 7th is represented in fig. 21. It shows that in the disc cells 



