Mivart might have adduced with equal appropriateness this resemblance as a special difficulty, or even their resemblance to the head and beak of a bird.

The avicularia are believed by Mr.

Busk, Dr.

Smitt and Dr.

Nitsche--naturalists who have carefully studied this group--to be homologous with the zooids and their cells which compose the zoophyte, the movable lip or lid of the cell corresponding with the lower and movable mandible of the avicularium.