ANIMAL RELATIONSHIPS. 
mals, separating the thoracic and 
visceral cavities. 
Dig'i ti grade (Lat. digztus, a fin- 
ger, and gradus, astep), walking 
on the toes without using the 
sole of the foot. 
Gas’tru la (Lat. dim. of gaster, the 
belly), an embryonic torm of 
animals belonging to the Meta- 
zoa. 
Mam/'‘mal (Lat. amma, breast), a 
255 
vertebrate animal whose female 
has milk-producing glands. 
Mor'u la (Gr. moron, a mulberry), 
an early stage from the growth of 
an egg. 
Plan’ti grade (Lat. p/anta, the sole 
of the toot, and gradus, a step), 
applied to animals which walk 
on the sole of the foot. 
Pter o dac’tyl (Gr. pteron, a wing, 
and daktylos, a finger), an ex- 
tinct flying reptile. 
