ox THE L>i;\ Kl.uJ'.MEXT ol' l.l.MlUs L( »Xcilsl'lXA. 7^ 



iiiiniber of" the furrows whidi I observod \va^ three.- The number 

 increased to five, tlièn ,^ix (in the stn^-e of figs, 17. 51, 57), new 

 fin-rows l)einfi- added posterior to tlie older ones. Tlie einbryo, soon 

 nftef liatehina-, lias only four pairs of rlic abdominal ap{)enda2'es, and 

 the second pair alone bears the gill lamellae. 



The [>e« iiliar a[)pendix, the flab.'lliim, -at. the exterior base of the 

 sixtVi ap|>endaL;-<î de\elops i'rom a small I'oiind protuberance (fig. 13). 

 The liomodynaiiKjus protuberances are also found in the segments of 

 t-he 2nd-5th ajipendages ; but they do not develop anv fiu-ther and 

 disa])pOMr. 



Nervous System. 



The lalcral liahc-; of the nervous system develop indepen- 

 dently of each other. Ividi lialf of the brain with its corresponding 

 ventral nerve-cord is ])roduced as a continuous long cord of epiblastic 

 thickening, just inside tlie base of tlie appendages (i\f^^. 12-1-1). It is 

 easy, howevei-, to distinguish the brain from the ventral nerve-cord. 

 When They aiv first formed, the former is vei-y much broader than the 

 latter, occnpying ahiiost rlie whole of tlie segment of the cephalic lobe, 

 Avhile the Neutral iierNc-ctn-d oc(ai{>ies onl\' about one tliird of the 

 bre:idtli of eadi a])pen(lage-beai'ing segmeiit (fig. 12). 



In the stage of fig. 12 we see most distinctly that the nervous 

 .system consists of peculiar cell-group-; like the ommatidia of tlie eve 

 (figs. 34, 3G, 38. 16). These ]>eciili:!i- cell-grou])s of the nerxoiis 

 system were first noticed by Patten. They (lisapjK'iir Avhen the \enlral 

 nerve-cord is divided into ganglia and begins to ])g separated frojn the 

 epiblast. 



A paired small invaglnatimi appears in the lateral part of thé 



