SALINELLA.[117]—This is another aquarium-animal, found by Frenzel in the Argentine, in an artificial saline solution with which he filled some aquaria. It measures .2 mm. in length, and has a somewhat flattened, barrel-shaped appearance. A single layer of ciliated cells bounds a central cavity opening at each end. Fission, and conjugation followed by encystment, have been observed. One form, _S. salve_, is known from salines taken from Cordova. NEMERTINEA BY LILIAN SHELDON Staff Lecturer in Natural Science, Newnham College, Cambridge. {99}CHAPTER V NEMERTINEA INTRODUCTORY—EXTERNAL CHARACTERS—ANATOMY—CLASSIFICATION—DEVELOPMENT—HABITS— REGENERATION—BREEDING—GEOGRAPHICAL DISTRIBUTION—LAND, FRESH-WATER, AND PARASITIC FORMS—AFFINITIES The Nemertinea form a compact group, the affinities of which have not been at present clearly determined. Several species were mentioned and described in the works of various naturalists during the latter half of the eighteenth century, though their anatomy was not understood until considerably later. The first mention of any member of the group was made by the Rev. W. Borlase in his _Natural History of Cornwall_, published in 1758. He gives a short description and a rough figure of _Lineus marinus_. From that time the increase in the knowledge of the group was very gradual. New species were from time to time described, but few of the descriptions could boast of much completeness, and many erroneous views were held until comparatively recent years. The group was very variously classified, but the general arrangement in early times seems to have been to unite it with the Planarians. Valuable contributions to the history of the development were made in 1848 and the few subsequent years by Desor,[118] Gegenbaur,[119] Krohn,[120] and Leuckart and Pagenstecher[121]; and more recently by Metschnikoff[122] and Salensky.[123] {100}Nemertines for the most part closely resemble one another in all essential points, though they differ considerably in size, colour, and external details. They vary in length from less than an inch to thirty yards, this extreme size being attained by _Lineus marinus_. [Illustration: FIG. 48.—_Lineus marinus_ Mont., from the living specimen in the coiled condition. Plymouth. × 1. _a_, Anterior end; _b_, posterior end.] [Illustration: FIG. 49.—_L. marinus_, from the same specimen as Fig. 48, in the expanded condition. _a_, Anterior end; _b_, posterior end.]