138 



THE TURBELLARIA. 



^§ 127, 128. 



CHAPTER VIII. 



ORGANS OF SECRETION. 



§ 127. 



No special organs of secretion have yet been found with the Turbellaria, 

 although these animals, and especially the Dendrocoeli, secrete from their 

 cutaneous surface an extraordinary quantity of mucus. '^^ 



CHAPTER IX. 



ORGANS OF GENERATION. 



§ 128. 



The Turbellaria propagate by transverse fissuration, and by the means 

 of genital organs. 



In the smaller Rhabdocoeli, which have no trace of genital organs, the 

 transverse fissuration is the rule.^^* It is, however, probable that at cer- 

 tain epochs of their lives, genital organs are developed, and therefore, that 

 they multiply also by eggs.*-"^ 



With both the larger Rhabdocoeli, and the Dendrocoeli, the genital and 

 copulatory organs of both sexes are situated upon one and the same individual, 

 so that they are capable , of self-impregnation ; but there is generally a re- 

 ciprocal copulation.^"* This genital apparatus is very complex, and as the 

 contents of its various parts have not yet been subjected to a careful analy- 

 sis, it is not positively certain that the right interpretation of them is 

 given. 



1 It is yet undecided wliether the subcutaneous 

 cell-like bodie3 of the DendrocoCIi have any relation 

 to this secretion. 



1 Dugis (Ann. d. Sc. Nat. XV. p. 169, PI. V. fig. 

 15) has observed a voluntary transverse fissuration 

 with Derostomum /eucops. I have been able to 

 follow the very regular fissuration of Microsto- 

 mum lineare, where each unseparatcd half of the 

 body began to halve again, and then these four jjieces 

 also each divided, and so finally the body appeared 

 worked by seven transverse furrows, into eight 

 divisions. 



I must here remark, to prevent an error, that I, 

 contrary to Orsted (loc. cit. p. 73), regard these 

 two mentioned species as distinct ; for Derosto- 

 mum leucops, Du^., is without the reddish brown 

 eye-dots and the prehensile organs, which are found 

 with Microstomum lineare, Orst. The wonder- 

 ful reproductive power of the sexless P/anariae, 



and which can be multiplied artificially by divisions 

 in all directions, would lead us to infer that they 

 propagate also from accidental divisions, to which 

 their vulnerable nature is constantly exposed.* 



2 Orsted (loc. cit. p. 21, Taf. III. fig. Si) and 

 Ehrenberg (Abhandl. d. Berl. Akad. loc. cit. p. 

 178, Taf. I. fig. 2, 3) aftirm to have seen ovaries, 

 testicles, copulatory organs, and eggs with Micro- 

 stomum lineare, and many other allied Rhabdo- 

 C'Sli, such as Gyratrir, Vortex, and Struns^ylo- 

 stomum ; but the details they have given are too 

 imperfect to allow definite opinions upon this or- 

 ganization. I must here ask if tliese animals have 

 not been confounded with the se.xless larv» whicli 

 multiply by fissuration Uke those of Medusae. 



3 Coition lias often been observed with Planaria 

 and Mesostomum, and has been figured by Baer, 

 Dugis, and Focke. 



* { § 128, note 1.] See Leidy (loc. cit.) ; he 

 found that with Phagocata {Planaria) gracilis, 



this subdivision could not be carried suocessfully 

 beyond three or four parts. — Ed. 



