E. Ray Lankester^ on the Gregarinida. 27 
impossible to speak of a species with that definite meaning 
which zoologists attribute to the word. A difference of ha- 
bitat is all that can be understood, generally speaking, from 
a specific name, among the Gregarinidse. Nevertheless, there 
are many forms which are very definite in their character, 
and appear to confine themselves to the same host. Such are 
M. pellucida, M. Aphrodites, G. Sieboldii, G. Heerii, G. Blattce, 
&c. There can be little doubt, however, that very many 
species have been named which are identical with others pre- 
viously known, but are merely found in a new bearer. The 
form which is met with in Ommatoplea and Convoluta (Tur- 
bellarians^ figs. 6, 7) occurs in many other Annelids, and 
I was surprised to find one of these in a specimen of Aphro- 
dita hystrix, whilst in twenty or thirty specimens examined 
by me in Guernsey not a single individual contained any 
other Gregarina. 
Gregarinida observed in Guernsey. — Having devoted some 
study to the Annelida obtained while with the dredging com- 
mittee of the British Association in Guernsey this year, I 
have a few additional notes to offer on the Gregarinida which 
infested some of the species. 
Monocystis Cirratuli, n. sp. (figs. 8, 9). — The perivisceral 
cavity of specimens of Cirratulus borealis, which were 
abundant in some muddy shores^ was invariably infested by 
large numbers of a simple form of Monocystis. No Grega- 
rinida have been previously observed in this Annelid, and 
hence I name the form after its bearer. The largest speci- 
mens were ^V^^ of inch in length. The young forms 
showed a striation of the investing membrane, and did not 
present that anterior enlargement which was noticeable in the 
more fully grown specimens. The length of the smallest 
observed, which was almost entirely free from granular 
matter^ was ttttt^Ii^ inch. (fig. 9). 
M. Nemertis, Kolliker. — In Ommatoplea and Convoluta, 
and once also in Aphrodita hystrix, I met with a form of 
Monocystis which may be referable to KoUiker^s species (figs. 
6, 7) . The most marked characteristic was the very frequent 
enlargement of the anterior extremity into a circular or 
spheroidal form ; this, however, was not persistent. The con- 
tained granules were coarse_, and the vesicle distinct 3 its 
average length was T^irth of an inch. Kolliker describes M. 
Neinertis from a Nemertian worm. It seems inadvisable to 
complicate the nomenclature by using a diff'erent specific 
name for the Gregarina of each genus of Nemertians, and 
hence I retain Kolliker^s name, though this form appears to 
differ somewhat from that which he figures. It is remark- 
