In the trunk an indication of a division into two segments makes its appearance shortly after the development of the præoral lobe. Before this period the proctodæum is established as a shallow pit immediately behind the insertion of the foot. The latter structure soon becomes pointed and forked (fig. 100, _t_). The complete establishment of the alimentary canal occurs late. The stomodæum (fig. 100) gives rise to the mouth (_m_), oesophagus and masticatory apparatus (_ms_). The mesenteron is formed from the median part of the hypoblast; the lateral parts of which appear to give rise to the great lateral glandular structures (_ld_) which open into the stomach, and to the ovaries (?) (_ov_) etc. The proctodæum becomes the cloaca and anus (_an_). The origin of the mesoblast is not certainly known. The shell is formed before the larva is hatched--an occurrence which does not take place till the larva closely resembles the adult. The early developmental stages of the male are closely similar to those of the female; and the chief difference between the two appears to consist in the development of the male being arrested at a certain point. The larvæ of Lacinularia (Huxley, No. 234) are provided with a præoral circlet of cilia containing two eye-spots[98], and a peri-anal patch of cilia. They closely resemble some telotrochal polychætous larvæ. [98] In Leydig's figure of the larva, _Zeit. f. wiss. Zool._ Vol. III. 1851, the eye-spots lie just outside the ciliated ring. Salensky has compared the larva of Brachionus to that of a cephalophorous Mollusc, more especially to the larva of Calyptræa on which he has made important observations. The præoral lobe, with the ciliated band, no doubt admits of a comparison with the velum of the larva of Molluscs; but it does so equally, as was first pointed out by Huxley, with the ciliated præoral lobe of the larvæ of many Vermes. It further deserves to be noted that the trochal disc of a Rotifer differs from the velum of a Mollusc in that the eyes and ganglia are placed dorsally to it, and not, as in the velum of a Mollusc, within it. The larva of Lacinularia appears to be an exception to this, since two eye-spots are stated to lie within the circlet of cilia. More important in the comparison is the so-called foot (tail), which arises in the embryo as a prominence between the mouth and anus, and in this respect exactly corresponds with the Molluscan foot.