362 THE AMERICAN NATURALIST. [VOL XXXIII: 
not by turning the animal over, but by transporting bodily the 
crustacean nerve cords and alimentary canal from the ventral to 
the dorsal side. By this simple process everything of importance 
that happens to lie between the dorsal and ventral surfaces must 
be either swept out of existence or forced into some corner where 
it undergoes extensive and complete degeneration. The result is a 
metamorphosis so profound that morphologists have completely failed 
to recognize the organs of the crab in their new forms and places. 
According to Gaskell, during the transition from crustacea to verte- 
brates, the crab’s heart is nearly crowded out through the back by 
Fic. x. Fic. 2. 
Fic. 1.— Diagrammatic cross-section of an arachnid (Limulus) in the head region, showing the 
relative position of heart, alimentary canal, endosternite, and principal peripheral nerves and 
commissures. 
Fic. 2. — Cross-section of a vertebrate illustrating Mr. Gaskell’s theory that the arthropod nerve 
cords, alimentary canal, and endosternite have been transferred to the original dorsal surface 
where the heart and alimentary canal undergo extensive deg tion. 
the dorsal movement of the nerve cords, although it still lingers in 
Ammocecetes, where he has detected it as “that peculiar elongated 
organ, composed of fattily degenerated tissue, which lies between 
the spinal cord and the dorsal median skin.” It is not clear whether 
it was the peculiar elongation of the organ or the presence of fat in 
it that enabled him to recognize the heart of Limulus in such an 
unusual place. Gaskell also proves, in the same manner, that the 
nephridia, or coxal glands of arthropods, have been disguised as the 
pituitary body of vertebrates; the genital part of the opercular 
appendages, as the thyroid glands and pseudo-branchial groove ; 
and he shows how the gigantic liver of crustacea is reduced to a mass 
