[Illustration: FIG. 67.—Free-swimming larva of _Gellius varius_, in optical section. _a_, Outer epithelium; _pi_, pigment; _x_, hinder pole. (After Maas.)] The reproductive elements are ova and spermatozoa, and are to be found in all stages in the dermal jelly. Dendy states that the eggs are fertilised in the inhalant canals, to which position they migrate by amoeboid movements, and there become suspended by a peduncle. The larva has unfortunately not been described, but as the course of development among the near relatives of _H. panicea_ is known to be fairly constant, it will be convenient to give a description of a "Halichondrine type" of larva based on Maas' account of the development of _Gellius varius_.[199] The free-swimming larvae escape by the osculum; they are minute oval bodies moving rapidly by means of a covering of cilia. The greater part of the body is a dazzling white, while the hinder pole is of a brown violet colour. This coloured patch is non-ciliate, the general covering of cilia ending at its edge in a ring of cilia twice the length of the others. Forward {173}movement takes place in a screw line; when this ceases the larva rests on its hinder pole, and the cilia cause it to turn round on its axis. Sections show that the larva is built up of two layers:— 1. "The inner mass," consisting of various kinds of cells in a gelatinous matrix. 2. A high flagellated epithelium, which entirely covers the larva with the exception of the hinder pole. [Illustration: FIG. 68.—Longitudinal section through the hinder pole of the larva of _G. varius_. _a_, Flagellated cells; _ma_^1, undifferentiated cell; _ma_^2, differentiated cell; _pi_, pigment; _x_, surface of hinder pole. (After Maas.)]