The shell and gizzard plates of Philine aperta were first described in 1616 by Fabius Colonna. Linnæus (1767) included the animal in his genus Bulla, and named it Bulla aperta. In 1772 Ascanius made a new genus, Philine, with P. aperta as type.

Cuvier (1810) created the order Tectibranchiata, and in the “Règne Animal” (1817) grouped in this order Pleurobranchus, Aplysia, Dolabella, Notarchus, Bulla, and Philine.

Fischer (1887) divided the Tectibranchs into the Cephalaspidea, the Anaspidea, and the Notaspidea; the first with a cephalic disc, the last with a dorsal shield, and the Anaspidea with neither.

St Kilda (Pl. V), the largest of a group of four islands located some 50 miles west of Harris in Latitude 57° 49′ N., Longitude 8° 34′ W., has an extreme length and breadth of 2½ by 1¾ miles and a circumference of about 8¾ miles. The highly indented coast-line is guarded by almost impregnable cliffs except in the Village Bay or Loch Hirta where there is a strip of sand a quarter of a mile long backed by a great storm-beach. The two principal inlets of the sea, Village Bay or Loch Hirta, and the Glen Bay open to the south-east and north-west respectively.

There have now been described some fourteen hundred species of Tabanidæ, of which, according to Surcouf (1924), more than a hundred are European. Biological studies of the family have by no means kept pace with those of its taxonomy, and there is available comparatively little information regarding the post-embryonic development of individual species.

Examination of the literature showed that none of the European species had been investigated with any degree of detail, and it was with the intention of supplying at least part of this want that the present study was undertaken in 1930. Because of its relative abundance from June to August in rural districts of Scotland, the common cleg, Hœmatopota pluvialis, L., was the species first chosen. The interest of this choice was considerably increased by the relisation that the biology of no species of Hœmatopota had previously been submitted to careful examination either in Europe or elsewhere.

The early developmental history of the ferret up to the present has not been made the subject of a detailed critical description. The early stages of certain other Carnivora have been described, and Professor Hill (1924) in the introduction to his paper, “The Early Development of the Cat,” gives a summary of the literature of the subject.

The only papers relating to the early development of the ferret are a short paper by Professor Robinson (1925) and four papers by Professor Mainland (1930, 1931a, 1931b, and 1932).

The genus Lyginorachis was proposed by Kidston (1923, pp. 18–19) to accommodate isolated petioles which, whilst their structure was similar in some respects to that in the petiole of Lyginopteris, could not be finally identified with the latter genus. Two species of Lyginorachis have been described (Scott, 1923, pp. 57-60; Crookall, 1931, pp. 27-34, pls. i-iii). Both came from Scottish Lower Carboniferous rocks; the one, Lyginorachis papilio Kidston and Scott, from the Cementstone Group (Calciferous Sandstone Series) at Norham Bridge on the Tweed, and the other, Lyginorachis Taitiana Kidston and Crookall, from the Auldton Limestone (Carboniferous Limestone Series) near Lesmahagow, Lanarkshire. Crookall also described a smaller and simpler petiole (loc. cit., pl. ii, fig. 3) as Lyginorachis sp., from the Cementstone Group at the Langton Burn, near Duns, Berwickshire.