PROSOMATIC SEGMENTS OF LIMULUS 253 
LIMULUS. VERTEBRATE. 
Segments. Appendages. Eurypterid appendages. eae Coelomic cavities. 
1 Chelicere or Ist Chelicerze 1 Anterior 
r locomotor. 
a) 2 2nd locomotor 
S 3] 8rd 7 : 
a Endognaths 2 Premandibular 
B\i 4] 4th i 
2 5 5th 55 
g 
tT] Ghilaria ” Hiaasen 4 |} Mandibular 
Genital 5 
; 8 Operculum ‘ 
3 9 ist branchial }operoulum en Focal 6 Hyoid. 
g 10 Qnd i, 2nd branchial 7 ist branchial 
2 11 8rd , 3rd 9 8 2nd, 
a 12 4th 3 4th ise 9 8rd 5 
Ss 13 5th . 5th 3 10 4th 3 
14 6th 5 11 
The second cavity would in reality represent four segments 
belonging to the 2nd, 3rd, 4th, 5th locomotor appendages, 7.e, the 
very four segments which in the Eurypteride are concentrated 
together to form the endognaths, and we should be justified in put- 
ting this interpretation on it, because, according to Kishinouye, its 
ventral portion forms the coxal gland, and, according to Lankester, the 
coxal gland sends prolongations into the coxa of the 2nd, 3rd, 4th, 
5th locomotor appendages. Similarly in the vertebrate, we find three 
head-cavities in-the region which corresponds, on my theory, to the 
prosomatic region of Limulus, (1) the anterior cavity discovered by 
Miss Platt, (2) the premandibular cavity, and (3) the mandibular 
cavity, which, if they corresponded with the prosomatic ccelomic cavities 
of Limulus, would represent not three segments but seven segments, 
as follows:—the anterior cavity would correspond to the first coelomic 
cavity, 7.e. the cavity of the cheliceral segments in both Limulus and 
the Eurypteride ; the premandibular, to the second ccelomic cavity, 
representing, therefore, the 2nd, 3rd, 4th, 5th prosomatic segments in 
Limulus and the endognathal segments in the Eurypteride ;, and the 
mandibular to the 3rd and 4th ccelomic cavities, representing the last 
locomotor and chilarial segments in Limulus, 7.¢. the ectognathal and 
metastomal segments in the Eurypteride. 
