MOLLUSCA 



195 



Fig. 182.— The 



Ocelli (Oc) of 

 the l.\rva of 



THE BrACHIO- 



POD, ClSTELLA 



(afterGladstone). 



ing seaweed, rocks and piles with a lace-like coating, and 

 multiply by budding. Some 1,800 species have been des- 

 cribed. The larva? of some species during their short freely- 

 swimming life before they settle on the rocks or mud, are 

 sometimes provided with rudimentary eyes. Thus the larvae 

 of Bugula turrila which have 4 or 5 slender flagellae, have 4 

 brilliantly red spherical eye-spots, 2 close to the pyriform 

 organ and 2 larger eye-spots located in the opposite hemis- 

 phere. The larva of the American Bugula flahellata has no 

 light-sensitive organs, but the European variety has 10 

 symmetrically arranged eye-spots (Xit.sche, 1870 ; Calvet, 

 1900 ; Grave, 1930 ; Lynch, 1949). 



BRACHIOPODA (lamp-shells), marine organisms of 

 great anticiuitj^ which have existed unchanged since the 

 Palaeozoic era ^ and are found in the seas in most parts of the world covered by 

 their shells firmly attached to rocks, are in some cases devoid of sense organs ; 

 in the freely-swimming larvte of others, patches of sensory epithelium form paired 

 eye-spots immediately over the cerebral ganglion which disappear when the larvie 

 become sessile (Cistella) (Fig. 182) ; but rudimentary eyes are exceptional 

 {Megerlia). 



Andre. Z. wiss. Zool., 95, 203 (1910). 

 Andrews. J. MorphoL, 5, 271 (1891). 

 Benham. Camb. Nat. Hist., London, 2, 



272 (1896). 

 Brunette. C. R. Acad. Sci. (Paris), 106, 



301 (1888). 

 Busch. Beobacht i'l Anat. u Entwicklung 



einiger Wirbellosen Seethiere (18.51). 

 Calvet. Trav. Inst. Zool., Montpellier, 8, 



22 (1900). 

 Faust. Biol. Bull, 35, 117 (1918). 

 Grave. J. MorphoL, 49, 3.55 (1930). 

 Herter. Biol. Tiere Deutsclilands, Lfg. 35, 



Teil 12b (1932). 

 Hess, W. N. J. Morplwl., 41, 63 (192.5). 

 Hesse, R. Z. wiss. Zool., 61, 393 (1896) ; 



62, 527, 671 (1897) ; 63, 361 (1898) ; 



65, 446 (1899) ; 68, 379 (1900) ; 70, 



347 (1901) ; 72, 565. 656 (1902). 

 Zool. Anz., 24, 30 (1901). 

 Das Sehen der niederen Tiere, Jena 



(1908). 



Hilton. J. entom. Zool., 13, 49, 55 (1921) ; 



16, 89 (1924). 

 Hj'man. Ainer. Mus. Xovit., No. 1005 



(1938). 

 The Invertebrates, London 2, (1951). 

 Lynch. Biol. Bull., 97, 302 (1949). 

 Nitsche. Z. wiss. Zool., 20, 1 (1870). 

 Parker and Haswell. Te.vtbook of Zoology, 



1 (1940). 

 Peters. Z. wiss. Zool., 139, 1 (1931). 

 Schmidt. Z. wiss. Zool., 72, 545 (1902). 

 Schroder. Abliandl. Senckenberg. Xatur- 



forsch. Ges., 35, 153 (1918). 

 Schulz. Zool. Anz., 95, 241 ; 96, 159 



(1931). 

 Steiner. Zool. Jb., Abt. System. Biol., 39, 



511 (1916). 

 Stossberg. Z. wiss. Zool.. 142, 313 (1932). 

 Taliaferro. J. e.vp. Zool., 31, 59 (1920). 

 Viaud. C. R. Soc. Biol. (Paris), 129, 1174, 



1178 (1938). 

 Bidl. biol. France Belg., 74, 249 (1940) ; 



77, 224 (1943). 



Brachiopod 



MOLLUSCA 



Among MOLLUSCS ('' soft bodied ") the most elementary types of 

 eyes are found and also the most elaborate forms that the simple eye 

 assimies, organs capable of a degree of resolution that the animal 

 cannot probably utilize ; between the two extremes almost every 

 imaginable form of eye is encountered. The characteristics of this 

 phylum are an unsegmented body with a muscular " foot " protruding 



1 Lingula, with fossil records dating some 500,000,000 years, is the oldest known 

 animal genus. 



