102 



ZOOLOGY. 



The Turlellaria are hermaphroditic, the ovaries and testes 

 with the accessory apparatus (Fig. 65) being present in the 

 same individual ; but in many forms the sexes are distinct. 



Little is known of the development of the flat-worms. 

 In a common marine Planarian, Stylochus elliptica (Girard), 

 which is about two centimetres long, and lives under stones 

 between tide-marks, north of Cape Cod, the eggs are depos- 

 ited in May and June, in a thin, viscid band, on stones and 

 sea-weeds. The eggs undergo total segmentation in four or 

 five days after they are laid. The larva is round, ciliated, 

 with a caudal nagellum. In eight or ten days after the 

 larva has hatched, it stops swimming about, and becomes a 

 ''mummy-like body," which Girard calls a "chrysalis." 

 In this state it floats about in the water. Its further his- 

 tory is unknown. 



In Leptoplana (Polycelis), according to Keferstein, the 

 yolk undergoes total segmentation as in Stylochus; the 

 outer layer of cells forms a blastoderm which surrounds the 

 more slowly growing cells within. Keferstein describes 

 and figures the various stages by which the spherical cili- 

 ated embryo attains the form of the adult, whose devel- 

 opment seems to be less in the nature of a metamorphosis 

 than that of Stylochus. 



The Planarians also in some species mul- 

 tiply by fission, and when cut into pieces, 

 according to H. J. Clark, each piece may 

 eventually become a well-formed Planarian. 

 Clark figm-es in his " Mind in Nature" two 

 Planarians derived from two sections of 

 Dendrocffilum lacteum, which became fully 

 developed within eleven days after the opera- 

 tion. Several Turbellarians are known to 

 undergo spontaneous fission. 



Catenula lemnce Duges, by transverse di- 

 vision, forms chain-like aggregations, and 

 oinefiivson a South Afri can species, C. quaterna, of 

 -After schmarda! Schmarda, has been found by him to have the 

 same habit. Fig. 66 represents two individuals (much 

 enlarged) in partial division, and a chain of five individ- 



the 

 ich 



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