CEYLON PEARL-INDUCING WORM. 127 
allowed, and the following notes indicate some of the results 
obtained. 
(1) The Free-swimming Stage. 
Although the plankton, both superficial and deep, has been 
collected and examined three times daily for two seasons, no Cestode 
larve have ever been found. This negative result falls in line with 
results obtained elsewhere. In any case it would be obviously 
impossible to identify an adult specimen from a free-swimming larva, 
even should such larve exist. So far as is known, only the larvee 
of Bothriocephalus latus aie ciliated and free-swimming, although it 
is possible that some larvee may be free-swimming without being 
ciliated. 
Little indeed is known regarding the earliest stages of many genera 
of Cestodes. 
Whilst examining the ripe proglottides from a specimen of Tetra- 
rhynchus rubromaculatus (?) obtained from the spiral valve of Trygon 
kuhli (which feeds exclusively on Polychetes and small bivalves), 
Inoted that the segmenting eggs, issuing in immense numbers from 
a rupture in a proglottis, were ciliated, a phenomenon I have not 
seen noted elsewhere. 
Up to the present nothing is known as to how the larve of T'etra- 
rhynchus unionifactor enter the oyster, and the same may be said of 
most marine species of Cestode larve. We do not know whether 
the larva is free-swimming, or whether it bores its way into the 
primary host, or whether it is ingested along with the food. In 
pearl fishing this question is of little importance, but the exact 
condition of affairs would be interesting as rounding off our 
knowledge of this interesting parasite. 
(2) The Globular Cyst in the Oyster. 
Figures of these cysts are given in Vols. II. and V., ‘‘ Ceylon 
Reports,” and they represent the earliest stages known of T'etrarhyn- 
chus unionifactor. They are considered to be post-hexacanth stages. 
They vary in size. Some are as large as a pin’s head, whilst others 
are quite microscopic. There are all sizes intermediate between 
them, but they are all exactly similar in structure and development, 
and their only point of difference is purely that of size. It has been 
shown that these larve multiply endogenously, that is to say, 
daughter cysts may arise within the parent cyst, and become liberated 
by a temporary rupture of the parental wall. Although the initial 
infection of the oyster is but slight, it may become extensive merely 
by endogenous reproduction of this kind, quite apart from a further 
infection from outside sources. Thisendogenous multiplication also 
accounts for the very varying sizes of larvee found in the oyster.* 


