222 The American Naturalist. [Mareb, 
vaginate. The entoderm (at least in several types) arises by 
delamination ; there is a large mid-gut, with well-developed 
glands (“liver”) while the proctodeum is short. The genital 
glands are reticulate and the spermatozoa are motile. 
There is little to be said upon the foregoing points, to which 
many more, applicable to both Xiphosures and some Arachnids, 
might be added. The exact seria] correspondence of the re- 
spiratory metameres in Limulus and the Scorpions have been 
enlarged upon by Lankester (81°), and considerable emphasis 
must be placed npon the fact that in all Arachnids the stomata 
are ventral, and are, in all instances, except in possibly the 
Solpugids and a few mites, are confined to the abdomen. 
These exceptions need new study. In the Scorpion, as in 
Limulus, the observations of Narayanan (’89) and Laume (90) 
show that the genital ducts are modified nephridia, and that 
they open upon the posterior surface of the first abdominal 
appendages. Delamination has been shown to occur in the 
Pseudoscorpions, Araneina, Phalangids and Limulus, as well 
as in the doubtfully Arachnidan Pycnogonids. 
Sup-Ciass I—GiGANTOSTRACA SEU MEROSTOMATA. 
Six pairs of cephalothoracic limbs around the mouth, the 
bases of the posterior pairs being masticatory. Behind e 
mouth a metastomial plate or pair of plates. Anterior edgè 
of carapax acute, its upper surface bearing median ocelli an ' 
a pair of lateral compound eyes. Respiration by mon y 
lamellate branchiæ (gill books) borne on appendages + 
the abdomen and protected by the enlarged first pair (oper: 
culum) which covers them. 
To these points, which cover both Xiphosures and pike 
terids, the following, derived from Limulus, : 
No salivary glands, no Malpighian tubes, no embryon! 
branes (amnion). 
In this Sere two orders are to be recognized, the ad 
terida (fossil) and the Xiphosures. In the latter are inc on 
the recent and fossil Limuloid forms. The difference ase in 
these is not readily formulated, but is readily recogni’ 
the specimens. The affinities of Cyclus are uncertain. 
may be added: 
c mel 
