ANIMAL RELATIONSHIPS. 
2 55 
mals, separating the thoracic and 
visceral cavities. 
Dig i ti grade (Lat. digitus , a fin¬ 
ger, 2L\\dgradus, a step), walking 
on the toes without using the 
sole of the foot. 
Gas'tru la (Lat. dim. of gaster , the 
belly), an embryonic iorm of 
animals belonging to the Meta¬ 
zoa. 
Mam'mal (Lat. mamma , breast), a 
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. planta, the sole 
of the foot, 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. 
