\o'2 3Ir. W. Nlcoll ou Tremalode 



althougli IIci'iliiKinii * notes tlic occnnviice oL' pearls in a 

 number of cockles examined by biin, to as lai-ge lui extent 

 as 8 in 25. 



In the foot the same cysts were foiind in mucli greater 

 nunibors, embedded beneatii the ei)iderinis in the muscular 

 tissue. They were most numerous near the ti]) and were 

 almost entirely confined to the lun-izoutal part. Occasionally 

 white concretions, .'L'-3 mm. in diameter, were met with in 

 the glandular part of the foot, but these luul no obvious 

 connexion with the occurrence of the cysts. 



The cysts vary from "21 mm. to *25 mm. in diameter. 

 They can be quite easily dissected out from the surrounding 

 tissue. The capsule is perfectly transparent and of a slightly 

 brownish cohmr. It consists of three pai-ts : the outermost 

 is a thin membrane and is separated from the rest by a space; 

 the middle layer is thicker than the internal, and the 

 whole thickness of the capsule is about "013 mm. It 

 contains the encysted stage of a Treraatode larva. By 

 the use of moderate pressure the capsule can be ruptured 

 and the D.stomid (PI. IV. fig. 5) set free. The anterior part 

 is broa'ler than the rest of the body, somewhat s])ade-shaped 

 in general outline and with a ridge (fig. 5, r.s.), in the form 

 of a horseshoe, bearing spines. The whole length of the 

 animal is "ZS-S mm. (minimum '6 mm.). The greatest 

 breadth of the anterior part is "IQ mm., while the rest of the 

 body varies from "l^ mm, in front to '08 mm. The body is 

 fiatteucd dorso-ventrally. 



Taere are two cup-shaped suckers, raised somewhat above 

 the surface of the body. The oral sucker, sitiated within 

 the ridge of spines, is smaller than the ventral, having a 

 diameter of "065 mm. The ventral lies in the middle of the 

 body, but nearer the posterior end, and measures "095 mm. 

 in diameter. Both suckers have a circular aperture. 



The ridge on the anterior end carries 29 spines arranged in 

 a single row. They are about -020 mm. long, Init three at 

 each end are shorter than the others. The ridge has rounded 

 ends and the two terminal spines on each side seem to lie 

 behind and below the adjacent ones. 



In addition, part of the body, from what may be called the 

 neck down almost to the level of the ventral sucker, is studded 

 with small hooks (fig. 5, c.s ) or spinelets. There are 30 or 

 40 transverse rows, and the hooks in one row alternate with 

 those in the next, so that diagonal rows are also formed. 



The mouth opens in the oral sucker and leads into a 



* Lancashire Sea-Fidheries Lab. Eep. for 190;J, p. 9-3. 



