550 J. S. KINGSLEY. 
(' 80 , p. 103) says that the antennal and shell glands agree in 
structure. Both terminate coecally, and have a long convoluted 
duct opening at the base of the corresponding pairs of 
appendages. 
The homology of the shell gland of the Crustacea with the 
segmental organs of the worms has been alluded to by many 
observers since Leydig first suggested it. Their similar origin, 1 
structure, position, and ducts, all seem to point to their 
homology. The strongest arguments against it are that the 
series contains at the most but two pairs, 2 and that no connec- 
tion with the body cavity exists. Recent authors (Leydig, ' 78 , 
Weissman, 74 , and Urbanowicz, ’ 84 ) seem to strongly favor 
the homology. 
The consideration of the evidence presented by the nervous, 
digestive, and circulatory systems I leave for another article ; 
that by the respiratory system has already been alluded to. It 
may be well here to combine the various points of similarity 
between Limulus and the Spiders, on the one hand, and the 
Crustacea on the other. In this I embody the results gathered 
by Professor Lankester in his valuable paper (’ 81 ), so often 
referred to. 
Limulus agrees with the Arachnida and differs from the 
Crustacea (1) in having six pairs of primitively post-oral 
pediform appendages ; (2) a seventh pair bearing the outlets 
of the reproductive organs ; (3) the ninth, tenth, eleventh, 
and twelfth, modified for respiratory purposes (the eighth 
pair in each shows a readily homologised structure, but dif- 
ferent functions) ; (4) in the character and structure of the 
upper lip ; (5) in the presence of a metastoma derived from the 
sternal portion of the sixth cephalothoracic segment. 
1 Reichenbach (’ 77 ) claimed that in Astacus the antennal gland was 
epiblastic in origin, a mistake which was corrected by Grobben (’79). Though 
Jshickawa (’85) repeats the statement for Atyephira. 
2 Huet (’82, I have not seen his final paper) describes a series of what he 
regards as segmental organs in the thorax of terrestrial Isopods (Oniscidae), 
which are arranged one pair in each segment. The caudal glands of Lere- 
boullet (’52) would appear to belong to the same series. Some of these have 
been found in the aquatic Oniscidae. 
