THE CEYI.OX rEAUr-OYSTEU. 293 



(R) OlJSEUVATTOXS OX TUE StrUCTUKE OF THE FllUlOTTS CVST.S 

 SURROUNDIXG TUE CesTODE LarV.E IX M AlUaAIiTIIEIlA 

 ViLGAlU.S. 



I may here add a few notes on the structui^e of the investing 

 cysts of Tyloce'phalmn ladijicans and 1\ nihius, bnsed upon niy 

 examination of Professor Herdman's slides and Dr. Kelaart's 

 material. 



In the eai'liest stages the cyst may be scarcely differentiated 

 fi'om the surrounding tissue, and about U'Ul or U-02 mm. thick. 

 This condition I find specially associated with a little-developed 

 })hase of the snjallei- larva T. minus, measuring 0*08 mm. in 

 diameter, and resembling B in figiu-e 4 on p. 21 of Part V. of 

 Herd man's lleport. In such thin cj'sts the nuclei of the fibres 

 are distinct, though hardly more so than those of the general 

 connective tissue of the oyster. One or two examples at this 

 and later stages were found in the n)uscular tissue without any 

 surrounding cysts at all, beyond a little of the interstitial tissue 

 of the muscle-bundles (PI. XXXIII. fig. 2). As the fibrous 

 capsule becomes thicker the nuclei appear at fii'St to become moi'e 

 abundant, and this may well be associated with the growth and 

 multiplication of the fibres. As a rule, the thicker cysts (0"2 mm. 

 thick and over) seem to be less densely nucleated, and may even 

 show very few nuclei, e.specially when they become higlily areolar 

 and edematous. The outer part of the cyst is usually ordinaiy 

 areolar connective tissue, Avith branched and ana.stomosing fibres 

 passing over, often quite imperceptibly, into the general con- 

 nective tissue of the body, such as occurs between the tubides 

 of the livei-. The cyst is, however, typically lined with several 

 layers of more regular parallel fibres, with abundant nuclei. In 

 some cases the fibres seem to coalesce to foi'm a dense almost 

 gristly substance, without obvious nuclei. 



The nuclei of the fibres are long and nariow, and ai-e situated 

 on their outside edges. 



In some cases the cyst appeal's to be entirely without nuclei, 

 and in such cases the fibres are often very thick, measuring as 

 much as 10 or 15 ^ in diameter. 



There is never, so far as I can see, any ti'ace of a lining 

 e})ithelium, though the cyst may be lined with a layei' of granules, 

 possibly derived from the Cestode or from the leucocytes of the 

 blood. 



In certain cases large dai-k-staining bodies were seen in the 

 areolfe of the fibi'ous connective tissue of the cyst, which suggested 

 parasitic Sporozoa, l)ut the pi-eparations did not allow of detailed 

 examination. 



A typical .section of the cyst of the smaller parasite, 

 2'ylocephalum minus, is shown on PI. XXXIII. fig. 3. 



This condition of things is very diflerent to that which is found 

 in the case of the pearl-inducing Trematode of Mi/tihis described 

 in 111}' paper (25). Here the parasite is surrounded by an 



