63 



cavities seem to be enlarged at the top by the efforts of a 

 crowd of Cyamus pacifiais which are seen to be nestling round 

 the cirripedes. According to Darwin's explanation the 

 burrowing is rather apparent than real, the pressure of the 

 group of cirripedes merely pressing inwards the skin of the 

 whale, and the epidermis as it forms being pushed upwards 

 between the nearly approximate shells. The young 

 Tuhicinella, though nearly cylindrical like the adult, has a 

 very much smaller aperture, and, as the growth takes place 

 at the base of the shell, the problem was how to account for 

 the widening of the aperture at the top. The solution is that 

 the upper margin suffers a gradual disintegration. For this 

 the structure of the shell is adapted, and specimens which by 

 reason of their broken edges might be thought to be damaged 

 and imperfect, are really in a condition essential to the 

 growth of the animal. Darwin says that probably " the 

 rapid downward growth of the shell, besides indenting the 

 whale's skin, at the same time slowly pushes the whole shell 

 out of the skin, and thus continually exposes the summit to 

 the wear and breakage which seems to be necessary for its 

 existence." It seems strange that the same rapidity of 

 downward growth should have the two opposite effects of 

 pushing the shell in and pushing it out. One would think it 

 sufficient that the growth of the cirripede shell should keep 

 pace with the formation of the upward pushing epidermis of 

 the whale. Darwin thinks that the slightly greater width of 

 the Ttibicinella shell above than below is, on his view, 

 beautifully explained, namely, " for the sake of facilitating 

 the protrusion of the shell ; for the ordinary conical shape of 

 sessile cirripedes, with the apex upwards, would have 

 rendered the pushing out of an imbedded shell almost 

 impossible ; on the other hand, we can see that the likewise 

 very peculiar, concentric, prominent belts may be necessary 

 to prevent too easy protrusion." But it is difficult to see 

 why a slightly conical shell would have found any special 

 difficulty in pushing out of the thinly surrounding walls of 

 the whale's epidermis. At worst the shape could only have 

 served the retarding purpose which Darwin attributes to the 

 concentric belts. When a Ttibicinella is taken out of the 

 whale's skin, these belts are found to have left a pretty sharp 

 impression, as sometimes the surface markings of a fossil are 

 imprinted on the matrix. The epidermis pushing between 

 the nearly contiguous shells will naturally take the impress 

 of their projections, but the shells pushing through the 

 epidermis would obliterate the stamp. 



The specimens sent me were from a Right Whal^ taken in 

 False Bay. 



