rROSOMATIC SEGMENTS of limulus 



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The second cavity would in reality represent four segments 

 belonging to the 2nd, 3rd, 4th, 5th locomotor appendages, i.e. the 

 very four segments which in the Eurypteridre 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 Piatt, (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 cudomic 

 cavity, i.e. the cavity of the cheliceral segments in both Limulus and 

 the Eurypteridie ; the premandibular, to the second ccelomic cavity, 

 representing, therefore, the 2nd, 3rd, 4th, 5th prosomatic segments in 

 Limulus and the endognathal segments in the Eurypteridre ; and the 

 mandibular to the 3rd and 4th ccelomic cavities, representing the last 

 locomotor and chilarial segments in Limulus, i.e. the ectoguathal and 

 metastomal segments in the Eurypteridce. 



