[5] The oldest observed larvæ (see Fig. 33) are characterised by the extraordinary length of the flagella of the outer antennæ, and in this respect resemble the larva of _Sergestes_ found by Claus near Messina (Zeitschr. für Wiss. Zool. Bd. xiii. Taf. 27, Fig. 14). This unusual length of the antennæ leads to the supposition that they belong to our commonest Prawn, which is very frequently eaten, and is most nearly allied to _Penëus setiferus_ of Florida. Claus’s _Acanthosoma_ (_l. c._ Fig. 13) is like the younger _ Mysis_-form of the larva figured by me in the ‘Archiv für Naturgeschichte,’ 1836, Taf. 2, Fig. 18, and which I am inclined to refer to _Sicyonia carinata._ [6] Van Beneden, who regards the eye-peduncles as limbs, cannot however avoid remarking upon _Mysis_: “Ce pédicule n’apparaît aucunement comme les autres appendices, et paraît avoir une autre valeur morphologique.” [7] ‘Archiv für Naturgeschichte’ 1863. Taf. 1. CHAPTER VIII. DEVELOPMENTAL HISTORY OF EDRIOPHTHALMA. Less varied than that of the Stalk-eyed Crustacea is the mode of development of the Isopoda and Amphipoda, which Leach united in the section Edriophthalma, or Crustacea with sessile eyes. The Rock-Slaters (_Ligia_) may serve as an example of the development of the Isopoda. In these, as in _Mysis,_ the caudal portion of the embryo is bent not downwards, but upwards; as in _Mysis_ also, a larval membrane is first of all formed, within which the Slater is developed. In _Mysis_ this first larval skin may be compared to a Nauplius; in _Ligia_ it appears like a maggot quite destitute of appendages, but produced into a long simple tail (Fig. 37). The egg-membrane is retained longer than in _Mysis_; it bursts only when the limbs of the young Slater are already partially developed in their full number. The dorsal surface of the Slater is united to the larval skin a little behind the head. At this point, when the union has been dissolved a little before the change of skin, there is a foliaceous appendage, which exists only for a short time, and disappears before the young Slater quits the brood-pouch of the mother.