220 



EMBRYOLOGY 



The pilidia of different Nemerteans differ from one another in shape 

 as the typical form described above is more or less distinctly developed. 

 In place of the fiagellum, Filidium gyrans bears a tuft of cilia at the 

 apex (Fig. 103). In Pilidium auriculatum (Leuckaet und Pagenstecher) 

 the two lateral lobes are only very slightly developed, and the Pilidium 

 brachiatum described by E. B. Wilson, which resembles P. aunculatum, 

 possesses, in addition to the two slightly developed lateral lobes, three 



Fig. 103. — Pilidium gyrans, with completely formed worm inside (combined from 

 two of BüTSCHLi's figures). Am, amnion ; D, intestine of the pilidium already sur- 

 rounded by the worm ; Ec, ectoderm of the worm ; M, mouth of the pilidium ; N, 

 fundament of the nervous system ; R, proboscis ; So, lateral organs. 



additional ones, which have arisen by indentations of the edge of the 

 umbrella. 



The Pilidium recurvatum found by Fewkes (No. 5) at Newport exhibits 

 a very aberrant form, which, by the absence of the lateral lobes, by the 

 lateral curvature of the upper part, and by the presence of a row of cilia 

 at the posterior end, acquires a striking resemblance to the Tornaria larva 



