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Rh gerardiae (Lacaze-Duthiers, 1865), sends such rootlets into its host as would justify the term Rhizothoracida. The small sinuous segmented body is enclosed, except for one small opening, in an enormous sac-like carapace, between the lamellae of which are protruded from the body the ovary and “liver,” both large, bifurcate and ramified. It is this sac-like and not valvular carapace, therefore, that justifies the term Ascothoracida. But Synagoga mira, Norman, 1888 (Brit. Assoc. Report for 1887), has the body covered by two nearly circular valves instead of a sac. Petrarca bathyactidis, G. H. Fowler (Quart. Journ. Mic. Sci., 1889, vol. xxx. pt. ii. p. 115), has a bilobed carapace, ventrally open; Dendrogaster astericola, Knipovitch (Biologisches Centralblatt, 1891, x. 707), is a multilobular sac, with apparently indistinct segmentation of the body proper on the dorsal side. For this highly problematic group the original authorities should by all means be consulted. The student may then be asked to compare the account of Synagoga mira both with the figure of the cypris-stage of Dendrogaster astericola and with the figure of the “indeterminate animal found on Gerardia,” about which Lacaze-Duthiers asks, “Is it the cypris-stage of Laura?” (Mém. Acad. Sci., 1883, xlii. 160, pl. 1, fig. 102). S. mira was found, like Laura gerardiae (fig. 3), in the Mediterranean, and found like it attached to an antipatharian. Its six pairs of limbs are not like the bare and simple feet of the Laura, but two-branched and setose as in the ordinary cypris-stage of the cirripede. The conclusion, therefore, from these facts and from the suggested comparisons, seems at least extremely probable that the question asked by H. Lacaze-Duthiers should be answered in the affirmative, and that S. mira is either the cypris-stage of Laura gerardiae or of some congeneric species. In Lacaze-Duthiers's highly-elaborated memoir it should be noticed that he uses the term “cirrhes” rather misleadingly, not for cirrhiform feet, but as the equivalent of setae. Also he gives two different reckonings of the segmentation, counting first eleven body segments without the caudal furca (p. 40), and then the caudal furca as itself the eleventh segment (p. 41). Of Petrarca the development is not yet known. The points of agreement and difference between it and Laura are carefully drawn out in the essay by Dr G. H. Fowler, who inclines to favour a close relationship between the Thyrostraca and Ostracoda. To the extreme development of the carapace in Laura, as compared with the segmented body, it would be difficult to find among crustaceans any analogy more striking than that of the great ovarial expansions in Nicothoe astaci, the little copepod parasite of the common lobster. The compactness of the class Crustacea is generally admitted; of the precise affinities of its subdivisions there is still much to learn.


 * (T. R. R. S.)

 THYRSUS (the latinized form of Gr., a stem or stalk) the wand or staff of Dionysus (Bacchus), the Bacchants and Maenads and the votaries taking part in his orgiastic rites. As commonly represented on the monuments it was a straight staff terminating in a pine cone, a ribbon or fillet being attached to the head below it. Another form terminated in a bunch of grapes and vine leaves, or ivy-berries and leaves. The pine-cone or bunch of leaves was sometimes supposed to cover the head of a spear, and the thyrsus was termed (see and ).  

THYSANOPTERA (, a fringe, and, a wing), a term used in zoological classification for a small order of the class (q.v.). The minute insects included in it, which haunt blossoms and leaves, are fairly well known to gardeners

by the name Thrips, a generic term used by Linnaeus for the four species of the group which he had examined and relegated to the order Hemiptera. The term Thysanoptera was first used by the Irish entomologist A. H. Haliday (1836), who made a careful study of the British species and recognized that their structural peculiarities required ordinal separation. H. Burmeister in 1838 also considered that these insects should form a distinct order, for which he proposed the name Physopoda, with reference to the bladder-like outgrowths (fig. 3) on the feet. Since then various authors have incorporated the Thysanoptera with one of the large orders, some, following Linnaeus, regarding them as Hemiptera, others grouping with them the Orthoptera or “Pseudoneuroptera.” But all recent students agree with Haliday and Burmeister in allowing the Thysanoptera to rank as a distinct order, showing affinities on the one hand with the Corrodentia (book-lice and biting lice) and on the other with the Hemiptera (cicads, bugs, &c.).

Characters.—The Thysanoptera, small insects with firmly chitinized cuticle, are recognized by the combination of imperfectly suctorial jaws—the mandibles acting as piercers and maxillae retaining their palps (see fig. 2)—with the presence of two pairs of excessively narrow wings (fig. 1), which are partly or completely surrounded by elongate delicate bristles forming a fringe. Other important structural features are mentioned below. In their life-history the Thysanoptera belong to the Exopterygote division of the (q.v.). The newly hatched insect closely resembles the parent, and the wing-rudiments appear externally on the second and third thoracic segments; but before the final moult the nymph remains quiescent, taking no food. Its condition thus recalls the pupal instar of the higher (Endopterygote) Hexapoda; and the Thysanoptera, though few in number, are seen to be of great interest to the student, exhibiting at once transition between the biting and the suctorial mouth, and the passage from “incomplete” to “complete” metamorphosis.

Structure.—The head is usually quadrangular in form with small but prominent compound eyes (fig. 2), whose facets are relatively large and convex; three ocelli may also be present on the vertex. The feelers are inserted close together (fig. 2) on the extreme front of the head; they exceed the head in length, but they are composed of only from six to nine segments, which are beset with prominent spines, some of the latter appearing to be organs of special sense. The mouth, with its jaws, forms a conical outgrowth which projects backwards, so that its apex lies beneath the prothorax. The labrum (fig. 2 c), which encloses the cone in front, is irregularly triangular in shape. Behind the mouth the two maxillae of the second pair are intimately