NOTES ON THE EMBRYOLOGY OP LIMULUS. 
549 
of the Arachnids and Limulus in a common group. It should 
be noted, however, that in complication, size, &c., the resem- 
blance between the glands of Limulus and those of the spiders 
is closer than between those of Limulus and those of the most 
limuloid of Arachnids, the scorpions. 
Packard (’75 a ), discovered these organs and suggested their 
homology with the segmental organs of worms ; Lankester 
(’ 82 , p. 101) said “ Possibly such coxal glands are the modified 
and isolated representatives of the complete series of tubular 
glands (nephridia) found at the base of each leg in the archaic 
Arthropod Peripatus ; ” while Michael (’ 83 ) suggests the 
homology of the glands in the Oribatidae with those of Scorpio, 
Limulus, Crustacea and Worms. Packard, in a later paper 
(’ 83 ), while failing to see the argument for the close asso- 
ciation of the Arachnids and Limulus derived from this 
organ, recognises the correspondence between the glands of 
Limulus and those of the Crustacea; but instead of making 
his comparisons with the “ shell-gland ” he refers only to the 
“ green-gland ” of the Decapods, an organ which occupies a 
different position in the body. His conclusion that “ The 
occurrence of these organs in the Arachnida, as well as in 
Crustacea, indicates the independent origin of these two 
groups of Arthropoda ” is intelligible only on the supposition 
that the word here italicised is a slip of the pen. This simi- 
larity of segmental organs in Limulus and the Arachnida 
neither loses nor gains in force by a comparison with the shell- 
gland of the lower Crustacea. This organ is a coiled tube with 
a coecal inner extremity and an efferent duct which opens at 
the base of the second maxilla (a position which I shall 
show further on is exactly comparable to that where the seg- 
mental organs of Limulus and the spider’s empty) but differs 
from the glands in the other groups in retaining its external 
opening through life. Thus the coxal glands of the one are the 
exact homologous of the shell-glands of the other. 
In the Crustacea two of the primitive series of segmental 
organs are found, one being the shell gland, the other the organ 
variously termed antennal gland or green gland. Grobben 
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