the orthonectida. 
227 
II. — Species Observed. 
I have had the opportunity of studying the species dis- 
covered by Macintosh. Lineus gesserensis is very common 
at Wimereux, as also its variety Lineus sanguineus y under 
stones, in oozy spots, which are accessible every day even 
during the neap tides. 
My attention was drawn to the parasite of this species, a 
rare one, on the whole, by my pupil and friend, J. Barrois, 
at the time when he was preparing in our laboratory his 
w’ork on the Nemerteans. But I could then, in the absence 
of sufficient material, do no more than verify a part of the 
observations of Macintosh, and rectify certain errors committed 
by this eminent zoologist, as I shall point out further on. 
In vain I have sought, on several occasions, for the para- 
site discovered by Refers tein in Leptoplana tremellaris ; 
and yet this Planarian is excessively common at AVimereux, 
in very nearly the same spots as Lineus gesserensis. Paul 
Hallez, Demonstrator in the Faculty of Sciences at Lille, 
who has dissected numerous examples of Leptoplana, has 
had no better luck than I in this search. 
A happy chance made me acquainted, in 1877, with two 
new species of Orthonectida, which I have been able since 
to obtain in sufficient abundance to make a nearly complete 
study of them, although some gaps still remain to be 
filled up. 
During the autumn of 1877 I had betaken myself to 
Wimereux in order to study the embryogeny of a species of 
Ophiura with condensed development. I had a choice 
between two species, Ophiothrix fragilis and Ophiocoma 
neglectay both equally common, hermaphrodite, and vivi- 
parous. Reasons of an entirely technical nature caused me 
to prefer the second. In opening hundreds of Ophiocoma, 
to extract from them the embryos, I discovered two species 
of Orthonectida which have enabled me to undertake the 
study of the group. Both are excessively abundant in 
the animal infested by them, but it is quite a rare thing 
to find an Ophiurid thus infested. According to my notes, 
each species may be found once among about eighty speci- 
mens of Ophiurids, so that one has the chance of finding 
one or other species once in forty specimens dissected.^ 
(Seance du 29, Octobre, 1870), a short preliminary notice of these 
animals. 
1 Besides these two species of Orthonectida, Ophiocoma neglecia presents 
at Wimereux a certain number of other parasites, which are interesting. 
1. A pretty Vorticella with a very short peduncle {Vorticella ophiocoma, 
