tiik ckylox i'eaul-oystku. 271 



(4) Examination of tiieCestode Theory of J'earl-Productiox. 



It, is unfortunjite tliat more firrures of pearls coiitaiiiing as luu-lfii 

 snjiposed Cestorles are not given in Prof, Htn-dniari's accoinit of 

 Pearl-formation. The only figures that represent the nuclei of 

 decalcifieil pearls examined eritire * as transparent objects a[)pf'ar 

 to be those on plate ii. in the Section on Peai-l-J^ro<liictiou in 

 Part V. of the Report, figui-es 5 and 7, figure 6 i-epresenting a 

 dead Cestode in a. ])a,rtia,lly calcified cyst (not, however, a pearl). 

 On p. 22 it is stated that these drawings, which ai-e i-eproduced 

 from Shipley and liornell's article upon the parasites of the Pearl- 

 Oyster in Part II, of tlie Report, are the work of Mr. Hornell, 

 and it is not evident from the text that Prof. Hei-dman l)ad ever 

 seen the specimens from which they wei-e made. Turning to these 

 same figures on plate i. of the article by Shipley a.nd Hornell on 

 the pai'asites of the Pearl-Oyster (Pait II. of the Repoit, figs. 5 

 (A) and 8 (B), (C), (i))), 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 repi-esenting the 

 Cestode larva enveloped in its " tough elastic and filjrous 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 larv;e witluMit examination of sections, and I caimot 

 help feeling that each of these figures is ca[)able of comparison 

 with the non-Cestodian centres of pearls described by me Ijelow. 



It is a remarkable fact that nowhere tlirougliout the Report is 

 there figured a section of a decalcified pearl showing the Cestode 

 remains in the nucleus, and to this fact I may add 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), whicli 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 Yermian 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 peai-1 figin-ed on plate ii. 

 fig. 4 A, in Part II, (Parasites) of the Report, and again in Part V. 

 (Pearl -Production), pi. i. fig. 5 k, c, d, & e, to the globular Cestode 

 larvje found in the Oyster is hardly enough to go upon. If such 

 a pearl consisted of a parasite thinly coated Avith nacre it 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 arc referred to bj- Southwell (42), p. 128, as "fi<jnres of sections 

 of (leciilcified pear's," but they are not described as such in the text; and they 

 certainly appear to be no more than drawings of the centres of pearls examined as 

 transparent objects. 



