192 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
5. Arachnida. 
Endosternite of Scorpio.* — Mr. H. M. Bernard compares tlie endo- 
sternite of Scorpio with the homologous structure in other Arachnida. 
He comes to the conclusion that these parts in Arachnids are apodema- 
tous structures due to fusion and compression of the cephalothoracic 
segments, and later specialized for muscular attachments. He considers 
that the endosternite of Limulus is a derivative of the ventral muscle- 
bands, and that it is homologous with that of Apus , and not with that of 
Arachnids ; and that it is clear there is no direct genetic relationship 
between Limulus and the Arachnida. 
Anatomy and Relations of Eurypteridae.t — Mr. M. Laurie, after 
giving an account of Slimonia, Pterygotus , Eurypterus , and Stylonurus, 
discusses the relations of Eurypterids among themselves, and suggests 
the following scheme : — 
Little can be usefully done in comparing the Eurypterids with 
Trilobites, for we know very little as to the details of the different 
appendages of the latter, and what little we do know of their anatomy is 
based on the more highly specialized forms. There appears to be little 
reason for regarding the Eurypterids as related at all closely to the 
Crustacea; to Limulus , which is a more primitive type than they, 
the relationship is not by direct descent, but through a compara- 
tively unspecialized ancestor ; this may possibly have been one of the 
Trilobites. 
The relationship of these three groups to “Arachnida” is shown in 
the table on the next page. 
* Ann. and Mag. Nat. Hist., xiii. (1893) pp. 18-26 (1 pi.), 
f Trans. Roy. Soc. Edinh, xxxvii. (1893) pp. 509-28 (2 pis.). 
