The peripheral ciliated layer of small cells becomes divided into two strata, of which the outer remains ciliated and forms the true epiblast: the inner probably forms the cutis. In it are developed rod-like bodies, which seem to be homologous with the thread-cells of the Coelenterata, so that if the views put forward in the previous chapter as to the similarity of the turbellarian and coelenterate larvæ are correct, the cutis corresponds with the deeper layer of the coelenterate epiblast. The mesoblast, like the epiblast, becomes divided into two strata. The outer one is stated to form the circular and longitudinal muscles; the inner one to give rise to a muscular reticulum, the spaces within which constitute the parenchymatous body cavity. The later changes are not of great importance. At a period slightly after the formation of the mouth and ganglia two pairs of stiff hairs become formed at the sides of the body. The embryo has by this time grown so as to fill up its capsule, in which however it continues rapidly to rotate, and also commences to exhibit active contractions. It next becomes hatched, and passes from a spherical to a flattened elongated form. The ventral oral opening is at first central, but soon, by a process of unequal growth, becomes carried towards the posterior end of the body. The pairs of stiff hairs in the meantime considerably increase in number. The remains of the yolk cells now disappear, and the enteric walls become more distinct. The alimentary canal, which is at first simple in outline like that of a rhabdocoelous Turbellarian, soon assumes a dendritic form. The young animal after these changes resembles its parent, except in the possession of only two pairs of eyes and in the absence of generative organs. Of the types with a complete metamorphosis the free larvæ of various species of Thysanozoon have been observed by Joh. Müller (190) and Moseley (189), and the complete development of Eurylepta auriculata has been studied by Hallez. [FIG. 87. LARVA OF EURYLEPTA AURICULATA IMMEDIATELY AFTER HATCHING. VIEWED FROM THE SIDE. (After Hallez.) _m_. mouth.] The stages within the egg of this latter type agree precisely with those already described in Leptoplana. After the formation of the mouth the body elongates, remaining however cylindrical. A fold forms on the anterior side of the mouth, giving rise to a large upper lip. Two posterior processes are next formed, and other processes soon arise, constituting the whole of those found in the free larva. The embryo next shakes off its egg membranes by a series of vigorous contractions. When free it has the form represented in the annexed figure (fig. 87). It is so similar to Müller's (fig. 88) and Moseley's larvæ that all three may be dealt with together.