NOTES ON THE EMBRYOLOGY OF LIMULUS. 
559 
lobes, in front of the rudimentary chelicerae and between the 
procephalic lobes. His figures clearly show however, that on 
account of their relations to the nervous system these lobes 
cannot be regarded as homodynamous either with the post-oral 
appendages, or with the appendages of insects. 
Assuming for the moment that the view that the antennae 
of Insects are not represented in either the Acerata or the 
Crustacea is correct, a comparison of the three groups may 
give us some further interesting points. In the following 
schedule only the anterior segments are included, and the appen- 
dages are called by their usual names, which no one regards as 
indicative of homologies extending through the whole Arthro- 
podan phylum. 
Hexafoda. 
Acerata. 
Crustacea. 
(1) Antennae 
. Absent 
Absent. 
(2) Mandibles 
. Chelicerae . 
Antennulae. 
(3) Maxillae 
. Pedipalpi . 
Antennae. 
(4) Labium 
. 1st legs 
Mandibles. 
(5) 1st pair legs . 
. 2nd pair legs 
1st maxillae. 
(6) 2nd pair legs . 
. 3rd pair legs 
2nd maxillae. 
(7) 3rd pair legs . 
. 4th pair legs 
1st maxillipeds. 
This comparison is a strictly serial oue and starts on the 
assumption that the first pairs of primitively post-oral appen- 
dages are homologous throughout. That this is true in the 
cases of the two last groups is, to my mind, very probable, but 
with regard to the Hexapods there is some reason for doubt. 
In following it out we are led to some interesting regional 
coincidences. It brings the end of the thorax of the Hexapod 
and Spiders into exact correspondence. In the case of the 
Crustacea a line of demarcation at the same spot is frequently 
visible, and one needs but to mention that it corresponds 
exactly to the posterior end of the head of the Tetradecapods, 
and is well paralleled in Squilla, and in the larva of Palinurus. 
In the Entomostraca a division at the same point may be seen 
in the larvae as also in the protozoea of Lucifer. These may 
all be analogies, and the fact that no such regional distinctions 
