Piirasites of lh>' Cockle and Mussel. 1 "* I 



examples it appears intensely l)l;ick, but in s;)me. the more 

 active and possibly the older, it is Ii;;liter in eolour. It con- 

 sists of two wide pouclies, nnitinj; posteriorly, continued by 

 a narrow tube, whieb opens terniinally by an excretory pore. 

 A pair of eyes [e.s.) is present, one on each side of the 

 oral sueker. Eaeb consists of a small crystalline rod with a 

 pigment-spot. Round tlu; aperture of the oral sucker arc 

 several minute j)apill;c. 



The fjenital system can hardly be made out in the liviiifif 

 animal, btit on death, when the tissues become more oj)a(jue, 

 a pair of testes {/s.) can be distinctly seon, one on each 

 side of, and somewhat behind, the ventral sucker. They 

 contain a mass of globular cells. From ea(;h testis a narrow 

 tube issues and joins its fellow from the other side at the 

 level of the sucker. From this point a single tube leads 

 forwards and opens jtist in front of the sueker. 



In atldition, in the living eerearia, a number (from 8 to 

 1;2) of globular cells {k.s.) can l)c seen in front of the ventral 

 sucker. These may possibly be the rudiments of the ovary. 

 With regard to the frequency of occurrence of the sporo- 

 eysts, in a sample of twenty cockles recently examined I 

 found every sijccimen infected and invariably the sporocysts 

 •were situated in tiie same position. The cockles were not of 

 full size, measuring on an average only 25 mm. 



It is evident that, as the eerearia can only perform creeping 

 movements, it must reach its next host in this manner. 

 Search in the mud, however, of the mussel-beds failed to 

 rev(al the migratory stage. I have also kept a number of 

 cockles and mussels togetlier in a tank for a considerable 

 time, until, in fact, the cockles died, but met with no better 

 success on examining the mud at the bottom. It is possible 

 that migration may only take place at a particular period of 

 the year. 



Although, in the cockle, the mantle-edge was free from 

 sporocy>ts, it was, nevertheless, by no means free from para- 

 sites. In this ease the infection took the form of inimerous 

 small globular cysts (Fl. IV. fig. 4), as many as 35 being 

 present in one specimen, although, as a rule, the number 

 did not exceed 10. They occurred usually in the inmost 

 fold of the mautle-edge, sometimes in groups of two or three, 

 but oftencr singly, and their distribution seemed to be general. 

 Thcv were situated in the loose conneeti\e tissue, just under- 

 neath the e[)ideruiis, but, as far as observed, their presence 

 gave rise to no pathological condition (except that there was 

 a slight proliferation of the cells in the neighbourhood). 

 There was no tendency to pearl-formation round these cysts, 



