Degree of Injury and Rate of Regeneration 519 
tional operculum has been removed at the proper level. ‘Thus 
with an additional injury to the individual the regenerating bud 
produces an organ larger in size and different in character from 
the original one. In my former papers I was concerned merely 
with the final results of the operations. A reference to my orig- 
inal notes however shows that there is a striking advantage in 
favor of the greater injury not only in the final size but also in 
the rate at which the material of the new operculum is prolifer- 
ated. ‘The same result was found in other species of Serpulids 
with dissimilar opercula such as Hydroides pectinata, H. uncinata, 
Serpula vermicularis, Apomatus ampullifera, etc. 
2 Rapidity of Differentiation of the Opercula in A pomatus 
ampullifera™ 
The branchie of the Serpulid Apomatus ampullifera are 
arranged in two semi-circular groups one on each side of the 
mouth. One of the branchie has a large terminal bulb which 
serves as the functional operculum. The corresponding branchia 
of the opposite side has a slight enlargement. Both circlets of 
branchie are readily thrown off at a breaking joint near their 
bases. In fact it is scarcely possible to operate on the animals 
without producing this autotomy. When the animal is otherwise 
uninjured the two circlets of branchiz are regenerated as described 
below. The two opercular branchie begin to show the terminal 
enlargements comparatively late in regeneration being at first 
wholly similar to the other branchiz. When however the greater 
part of the posterior region of the body 1s removed at the same 
time the two branchial circlets begin to regenerate from the breaking 
joints as before but the opercular enlargements appear at the very 
beginning of regeneration. In this case an additional injury to 
the individual produces an acceleration of the rate of differentia- 
tion of the opercula. 
The observations on the opercula of the Serpulid worms as 
well as simultaneous observations on the chele of the Crustacea 
1 Journal Exp. Zoél., 1905, pp. 77-80. 
