THE CEYLON PEARL-OYSTER, ial. 
(4) EXAMINATION OF THE CESTODE THEORY OF PEARL-PRODUCTION. 
It is unfortunate that more figures of pearls containing as nuclei 
supposed Cestodes are not given in Prof. Herdman’s account of 
Pearl-formation, The only figures that represent the nuclei of 
decalcified pearls examined entire * as transparent objects appear 
to be those on plate ii. in the Section on Pearl-Production in 
Part V. of the Report, figures 5 and 7, figure 6 representing a 
dead Cestode in a partially calcified cyst (not, however, a pearl). 
On p. 22 it is stated that these drawings, which are reproduced 
from Shipley and Hornell’s article upon the parasites of the Pearl- 
Oyster in Part II. of the Report, are the work of Mr. Hornell, 
and it is not evident from the text that Prof. Herdman had ever 
seen the specimens from which they were made. Turning to these 
same figures on plate i. of the article by Shipley and Hornell on 
the parasites of the Pearl-Oyster (Part I]. of the Report, figs. 5 
(A) and 8 (B), (C), (D)), we find them described in the Explana- 
tion of the Plates as the nuclei of decalcified pearls; but the same 
figures are referred to in the text, p. 80, as representing the 
Cestode larva enveloped in its “tough elastic and fibrous capsule 
of spherical form, derived from the adjacent connective tissue 
cells.” 
It is, I think, hazardous to identify these figures as the remains 
of Cestode larve without examination of sections, and I eannot 
help feeling that each of these figures is capable of comparison 
with the non-Cestodian centres of pearls described by me below. 
Tt is a remarkable fact that nowhere throughout the Report is 
there figured a section of a decalcified pear] showing the Cestode 
remains in the nucleus, and to this fact I may fale my own 
observation that of all the pearls sectioned in situ by Prof. Herd- 
man, numbering about 25 (not counting some minute clustered 
muscle-pearls), which he kindly sent me to examine, I could not 
find a single nucleus that I was able to accept as being a Cestode 
or other Vermian parasite. The characters of the nuclei in these 
preparations are described in the part of the paper which deals 
with my own researches. 
The superficial resemblance of the pearl figured on plate ii. 
fig. 4.4, im Part II. eo) of the Report, anda gain in Part V. 
(Pear]- Production), pl. i. fig. 5 &, c, d, & e, to the globular Cestode 
Jarve found in the Oyster is hardly enough to go upon. If such 
a pearl consisted of a parasite thinly coated with nacre if would 
probably be dark and valueless and not a “fine pearl,” for the 
yellowish-brown dead tissue of the Cestode should be clearly 
visible through the nacreous coat. It is not stated whether this 
pearl was decalcified and sectioned to test whether the resemblance 
was more than “ skin deep.” 
* These figures are referred to by Southwell (42), p. 128, as “figures of sections 
of decalcified pearls,” but they are not described as suc h in the text; and they 
certainly appear to be no more than drawings of the centres of pearls examined as 
transparent objects. 
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