386 



WILLIAM PATTEN. 



The development of the cephalic lobes in Limulus 

 represents a still greater modification of the Acilius type. 

 There is a well-marked transverse furrow at the anterior end 

 of the cephalic lobes^ probably representing, as in Scorpio, 

 the fused ganglionic pits of the first segment. Behind the 

 furrowj on either edge of the cephalic lobe, is a small pore 



Fig. 6. — F. Median eye of Scorpion about, ready to hatch, seen from 

 above as a transparent object (compare Fig. 5, £). A'-E' indicate 

 planes of sections A-E. eg. Corneagen. cp. Capsule, d. Cuticula, 

 on ends of primitive retinal cells. D>\ Diverticulum (?). ec. Ectoderm. 

 ?2/j. Neuropore. o/j.w. Optic nerve. pg.c.2inAr'. Pigment-cells, derived 

 from primitive retina, p. r. Primitive retina. /. Ditto. /'. Secondary 

 retina. 



leading into a long narrow tube. The latter may be regarded 

 as extremely deep optico-ganglionic invaginations ; they corre- 

 spond, in part at least, to the invaginations of the second 

 segment of Scorpio. The position of the pits is the same in 

 both cases ; besides, just as in Scorpions, the mouths of the pits 

 move toward the median ventral line, forming an unpaired 

 pore leading into the cavity of the optic tubes. The latter 

 have, meantime, united to form an unpaired tube with a swollen 

 blind end from which the median eyes are finally developed 

 (Fig. 7, b). The walls of the tube give rise to the optic nerve 

 to the median eye, and the basal portion of it to the optic 

 ganglia (Fig. 10,/. and/.). 



There is a third ganglionic invagination, much like the 

 corresponding one in Scorpio, which gives rise to the optic 

 ganglion of the lateral eyes (Fig. 7, g. v^.). This gang- 



