280 DR. H. LYSTER JAMESON ON 
while in Part V. of the Report, p. 14, he and Hornell say :— 
“Some of our Ceylon Pearl- Oyster parasites very closely 
resemble the figures given by Giard” |i. e. of Seurat’s lar va] 
‘“and possibly may also belong to the genus Cyathocephalus 
| Tylocephalum|, although most of them are certainly Tetra- 
rhynchids ” ; 
and on pp. 16-17: 
“Tt is possible, however, that more than one species of 
Cestode is represented—one is certainly a species of Tetra- 
rhynchus (Rhynchobothrius), and another is probably the 
saine genus, or may possibly belong to Cyathocephalus ... .” 
Later on, however (p. 20), Herdman and Hornell reject the 
idea that the globular larvee may be Tylocephala or allied genera, 
and, in discussing the opinions of Giard and Seurat on the 
systematic position of Seurat’s larva, they say that they regard 
the terminal invagination, not as a sucker with a papilla on its 
floor, but as 
“the opening in a hood or depression formed by the 
sinking of the scolex into the front of its vesicle. The 
changes of shape which we observed in this larva in the living 
state, the protrusion and retraction of the papilla-like part 
which we regard as the anterior end of the scolex, agree with 
this interpretation. Consequently, we are of opinion that this 
larval Cestode is not one of the Monobothria—that it belongs 
to neither the Pseudophyllidea nor the Tetraphyllidea, but is 
a young Tetrarhynchid belonging to the Trypanorhyncha, and 
we give here (fig. 4) a series of diagrams in order to show 
the positions that we suppose our ‘stages to occupy in the 
development of such a form.” 
Shipley and Hornell (Herdman’s Report IT. p. 80) call attention 
to the resemblance of older examples of the larger larva (7'ylo- 
cephalum ludificans) to Seurat’s form, and think there is little 
doubt that they are at least generically the same (p. 82). Again, 
Southwell says (39, p. 169) : 
“Tt would certainly appear more probable, as well as 
simpler, for this larva to develop into a Tylocephalum (as is 
believed by Seurat) than into a Tetrarhynchus.” 

Again, Southwell, speaking of the great scarcity of the adult 
of Tetrarhynchus unionifactor in Elasmobranchs taken by trawling, 
says (42 p. 130): 
“Tt would almost appear that this fact in itself is sufficient 
proof that the adult of the pearl-inducing worm is not 
Tetrarhynchus unionifactor.” 
But at the foot of the same page he reverts to the position 
that it is a Tetrarhynchus. 
[22] 
