DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
787 
fourth pair (Fig. 185, p l .) arise in front of and slightly below the third in the same 
manner as the other buds. 
Up to this point the order of succession is almost invariable. The sequence in the 
appearance of the remaining buds is subject to considerable variation, though their 
position is definite and constant. They make their appearance in the angles between 
the buds already formed, and in the angles between these and the primary polyp ; this 
will be rendered clear by an inspection of figs. 186 to 188. 
In fig. 185 a fifth pair (p 5 .) have appeared between the first and second. In 
fig. 186 two additional pairs (p 6 . and p 7 .) have appeared; one pair (p 6 .) are placed in 
the posterior angles between p 3 . and the primary polyp, and the other ( p 7 .) are 
between p 1 . and p 3 . 
Fig. 187 is a still older colony in which five new pairs, besides the seven of fig. 186, 
have appeared. 
Of these new pairs p 13 . are placed in front of the entire series, while the remaining 
four (p n .,p 10 ., p 9 ., and p 8 .) are placed in the angles between p 3 .-p 4 ., pb-p 5 , p 5 .-p 2 ., 
and p 3 .-p 6 ., respectively. 
Fig. 188 is a still later stage with the tentacles retracted. 
The buds are designated as before. Only one additional pair has appeared (p 13 .), 
but those of the last stage have greatly increased in size, as may be seen by 
comparing the corresponding buds marked p 10 . in the two figures. 
The colony has now assumed the form of a flattened disc, with polyps in various 
stages of growth situated all around the edge. This form results from the circum¬ 
stance that the secondary polyps grow out laterally away from the primary polyps, 
and the younger polyps borne in their angles are thus carried further and further 
away from the centre of the group. The longitudinal axes of the secondaiy polyps 
radiate in every direction from the central point. The posterior part of the axial 
polyp ( ped .) may now be recognised as the peduncle of the colony. 
It has already been noted that the third bud lies a little below the level of the first, 
and the fourth a little below the third. The buds are therefore arranged on each 
side in an oblique line, extending forwards and downwards. This line is continued by 
succeeding buds so that the anterior buds finally come to lie partly on the lower side 
of the axial polyp, as at p 13 . in fig. 188. The two lines of buds finally meet one 
another at the ventral side of the axial polyp. The latter meanwhile bends gradually 
upwards so that the two lines of buds are kept nearly horizontal, and when they 
meet are situated at the anterior edge of the disc, and not at its lower side. The 
axial polyp is thus cut off entirely from the edge, and now rises from the upper side 
of the disc. This process will be rendered clear by an inspection of fig. 189, where ax. 
designates the axial polyp, andp 13 .,p 13 ., the foremost pair of lateral buds which have 
united behind the axial polyp at the point x. In the angle between p 13 ., p 13 . has 
appeared a median bud which completes the outline of the disc in front. 
The portion of the axial cell which is included in the disc, forms the “ polyp-cell ” 
