| Description | Slide shows four diagrams regarding cleavage stages in snails.
Diagrams are labelled 'a', 'a'', 'b', and 'b''.
The explanatory text below the diagrams reads: 'Fig. 92. - Above, the first cleavage stage in a snail, showing position of spindles for next cleavage division in left-handed (sinistral) cleavage (a) and right-handed (dextral) cleavage (a'). Below, same after cleavage; b, sinistral type, b', dextral type. (After Morgan.)'. |