ROTIFER A. 185 



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 ditference between the two 

 appears to consist in the development of the male being arrested 

 at a certain point. 



The larvae of Lacinularia (Huxley, No. 234) are provided with 

 a prseoral circlet of cilia containing two eye-spots 1 , and a perianal 

 patch of cilia. They closely resemble some telotrochal polychaetous 

 larvse. 



Salensky has compared the larva of Brachionus to that of a 

 cephalophorous Mollusc, more especially to the larva of Calyptrsea 

 on which he has made important observations. The praeoral 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 praeoral lobe of the 

 larvae 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, 



If Salensky 's comparison is correct, and there is something to 

 be said for it, the foot or tail of Rotifers is not a post-anal portion 

 of the trunk, but a ventral appendage, and the segmentation which 

 it frequently exhibits is not to be compared with a true segmen- 

 tation of the trunk. If the Rotifers, as seems not impossible, exhibit 

 crustacean affinities, the 'foot' may perhaps be best compared with 

 the peculiar ventral spine of the Nauplius larva of Lepas fascicularis 

 (vide Chapter on Crustacea) which in the arrangement of its spines 

 and other points also exhibits a kind of segmentation. 



BIBLIOGRAPHY. 



(232) F. Colin. " Ueb. d. Fortpflanzuug von Eiiderthiere." Zeit. f. wiss. ZooL 

 Vol. vii. 1856. 



(233) F. Colin. " Bemerkungen ii. Eiiderthiere." Zeit. f. iciss. Zool. Vol. ix. 

 1858, and Vol. xn. 1862. 



(234) T. H. Huxley. "Lacinularia socialis." Trans, of the Microscopical 

 Society, 1853. 



(235) Fr. Leydig. "Ueb. d. Bau u. d. systernatische Stellung d. Baderthiere." 

 Zeit. f. wiss. Zool. Vol. vi. 1854. 



(136) W. Salensky. "Beit. z. Entwick. von Brachionus urceolaris." Zeit. f. 

 wiss. Zool. Vol. xxii. 1872. 



(237) C. Semper. "Zoologische Aphorismeii. Trochosphasra aequatorialis." Zeit. 

 f. wiss. ZooL Vol. xxii. 1872. 



1 In Leydig's figure of the larva, Zeit. f. wiss. Zool. Vol. m. 1851, the eye-spotd lie 

 just outside the ciliated ring. 



