PLUMULARIANS. 
235 
however, we find a deviation from this primitive arrangement. 
In this species the primary plume gives off at intervals a 
number of secondary plumes or plumules, which occupy the 
place of ordinary pinnse, and in this way a ramified composite 
structure is formed. Some of these plumules exhibit a curious 
peculiarity ; every here and there a pinna occurs, which is 
destitute of calycles, but carries a line of sarcothecse on each 
side (PI. CX., fig. 5 b 6), and near the base a single reproductive 
capsule. Such abnormal pinnse are always curved inwards, so 
as to bend over and in some measure shield the capsule. They 
occur at intervals, and alternately on each side of the plume, 
two of the ordinary pinnse intervening between each pair. In 
other respects the plumule is perfectly normal. 
In another species (African *) these modified pinnse alternate 
on both sides of the plumule with the ordinary pinnse. In yet 
another form (Australian) f all the pinnse on the plumules pro- 
ducing the reproductive bodies are thus modified ; the calycles 
with their polypites have altogether disappeared, and only the 
lateral “ calicetti,” much elongated, remain. All the pinnse are 
now reduced to the condition of serrated appendages, which 
bend forward to meet one another, and overarch the capsules at 
their base. In this case the plumule is a corbula , minus the 
membrane which unites the lateral appendages. In our own 
“Podded Coralline ” (. Aglaophenia pluma ), this element is sup- 
plied ; a horny outgrowth from the modified pinnse binds them 
all together, and completes the closed casket in which the re- 
productive members of the colony are lodged (PI. CX., fig. 4). 
The various stages in the evolutionary process are here 
clearly traceable. We may note the plumule changing its 
character little by little through a series of intermediary forms, 
until at length it passes into the corbula , and . so follow the 
organ step by step from its rudiments to its perfect state. 
We have first an occasional pinna modified as a support and 
shelter for a reproductive capsule; then the number of such 
pinnse increases until the entire plumule is involved in the 
change and becomes altogether subservient to the protective 
function; then the pinnse, hitherto disjunct and independent, 
unite, and the plumule, as it were, disappears in the pod-like 
corbula . There is no serious gap in the morphological re- 
cord. 
One or two variations upon the ordinary structure occur. 
Thus in the finest of our British Plumularians the 66 Sea-Palm ” 
( Aglaophenia myriophyllum ), the lateral appendages of the 
beautiful open corbula with which it is furnished differ in 
* Aglaophenia patula, Kirchenpauer. 
f Aglaophenia ramosa , Busk. 
