138 NEW YORK STATE MUSEUM 
stages of the eurypterids are described 1n detail now for the first time, it 
appears very appropriate to test the hypothesis of this arachnidan rela- 
tionship by the ontogenetic evidence now available. Kingsley [1893, p. 
228] cites, in his full discussion of the agreements and differences between 
Limulus and the crustaceans on one hand and the arachnids on the other, 
these six points of agreement: 
A branchial respiration 
The possession of biramous appendages 
The absence of malpighian tubes 
The absence of salivary glands 
The absence of embryonic envelops 
The presence of compound eyes 
Nm BB WH NO H 
and 28 points in which Limulus and the arachnids agree, and in which 
both differ from the other “ Tracheates’’ (Hexapoda and Myriapoda). 
The following of these points are considered as of special importance for 
the association of Merostomata and Arachnida: 
(1) The numerical homologies of segments and appendages; (2) the 
exact homologies existing in the respiratory organs; (3) the fact that the 
cephalothoracic appendages are pediform, the basal joints serving as jaws; 
(4) the presence of true nephridia opening in the base of the third or fifth 
pair of appendages or in both; (s) genital openings in the seventh (or more 
probably eighth) segment of the body; (6) extreme length of the midgut; 
(7) presence of an internal structure, the entosternite; (8) inclusion of the 
ventral nerve cord and its nerves in the external artery and its branches; 
(9) the close similarities in the central nervous system. 
The last chapter of Thorell’s paper on A Sulurian Scorpion from 
Gotland is entitled: Are the Merostomes Arachnids ? Here the author 
gives a critical discussion of these points of resemblance and concludes that 
the characters on the basis of which the merostomes have been considered 
as nearly related to the scorpions are “fully counterbalanced by the dif- 
ferences exhibited in the structure of the organs of respiration and by the 
fact that the scorpions and all the higher Arachnida are provided with 
