62 PATTEN. [Vov. XII. 
the body is a striking fact, and it should also be observed 
that each individual part of the embryo, and especially the 
ends, tends to assume the shape of a single or double V, 
characteristic of entire embryos 
undergoing atrophy by median or 
apical fusion and degeneration. 
In comparing these variations in 
Limulus, Fig. 6, with the normal 
conditions in other arthropods, I 
a will merely bring to mind the fol- 
lowing facts, to which others might 
be added. 
(z) In the first region we have to 
recall the absence, or median fusion, 
or degeneration, of appendages at 
the anterior margin of the cephalic 
lobes, especially in insect embryos, 
and the absence or fusion or de- 
generation of the anterior pairs of 
ocelli in arachnid embryos (scor- 
pions, spiders, Limulus) and the 
Ee: great development of the antennae 
Diagram to\show Jines/and regions'of ana dateral eyes arising sro athe 
most frequent degeneration. The 
lateral constrictions indicate potential posterior margins, as in insects and 
fission planes due to partial median 1 
fusion. The cross-lines indicate the crustacea. 
relative (weakness of: the /dittercat 7) he reductionwandenhemine- 
soaks quent median fusion of the ap- 
pendages just back of the mouth in insects, crustacea and 
arachnids, and the much greater size of those at: the posterior 
end of the thorax. The frequent absence of the chelicerae 
in Limulus is to be compared with the small size of these 
appendages in the vast majority of arachnids. The manifest 
weakness of the first three pairs of thoracic appendages in 

=a a 
Bt SzSs 
GP 






1 The degree of median fusion may therefore be taken as an index of the 
original order of serially homologous organs. Applied to vertebrates, this would 
indicate that the most anterior sense-organ is the pineal eye, followed by the 
olfactory organ and the lateral eyes, just as is the case in Limulus. This 
harmonizes with the conclusions that I have reached on anatomical and embryo- 
logical grounds of an entirely different nature. 
