KESPIRATOEY ORGANS IN AEANEJ]. 
87 
the homologies of the abdominal appendages of the eighth 
to thirteenth somites in Limulus and the three pulmonate 
orders of A.rachnida, based upon the most recent embryo- 
logicad researches. The segmental homologies given in this 
table agree with that of the same six somites given by Borner 
( 02 , pp. 456, 457), and may be taken, so far as the pulmonate 
Arachnida are concerned, as sufficiently established, whereas 
the homologies of these segments in most of the Tracheate 
orders of Arachnida cannot be considered as satisfactorily 
established, since the necessary embryological evidence is 
wanting and that afforded by comparative anatomical research 
insufficient. 
The most important point in connection with this question 
is the position of the genital opening. 
(1) Aranem. — I have shown in a previous paper (’95) 
that the genital ducts in Attusfloricola are formed out of 
part of the coelom of the pulmonary somite and open extern- 
ally into the interpulmonary (epigastric) in-folding, which lies 
between the eighth and ninth somites. The genital segment 
in Dipneumonous spiders is, therefore, identical with the first 
pulmonary segment, which has been shown to be the eighth 
post-oral by all the most recent investigators (Kishinouye, 
’90; Simmons, ’94; Jaworowski, ’94; and myself, ’95). 
(2) Scorjiiones. — Brauer (’95) has clearly shown that 
the seventh somite in the scorpions had been overlooked by 
previous authors, and that the genital operculum belongs to 
the eighth somite, the pectines to the ninth, and the four 
pairs of lungs to the tenth to thirteenth. Pereyaslawzewa 
(;07) also places the four pairs of lung-books in the tenth to 
thirteenth somites (pp. 174-176). 
The homologies of the abdominal appendages in scorpions 
and spiders given in the table on p. 86 may, therefore, be 
considered as fully established by embryological evidence. 
We have thus the remarkable fact, which I pointed out 
before (’95), that none of the lung-books in scorpions 
are actually homologous with the tw'O pairs in 
spiders, and further, the two pairs of lung-books in spiders 
