138 



THE TUEBELLAEIA. 



^^ 127, 128. 



CHAPTER VIII. 



ORGANS OF SECKETION. 



§ 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 imdecided whether the subcutaneous 

 cell-Uke bodies of the Dendrocoeli have any relation 

 to this secretion. 



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

 15) has observed a voluntary transverse fissuration 

 with Derostomum /eiicops. I have been able to 

 follow the very regular fissuration of Microsto- 

 mum lineare, where each unseparated half of the 

 body began to halve again, and then these four pieces 

 also each divided, aud 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. Dug., is without the reddish brown 

 eye-dots and the prehensUe organs, which are found 

 with Microstomum lineare, Orst. The wonder- 

 ful reproductive power of the sexless Planariae, 



and which can be multiplied artificially by divisions 

 in all du'ections, would lead us to infer that they 

 propagate also from accidental divisions, to which 

 their vulnerable nature is constantly e>q)0sed.* 



2 Orsted (loc. cit. p. 21, Taf. IH. fig. 53) and 

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

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

 testicles, copulatory organs, and eggs with Micro- 

 stomum lineare, and many other allied Rhabdo- 

 cutili, such as Gyratrix, Vortex, and Strongylo- 

 stomum ; but the details they have given are too 

 Imperfect to allow definite opinions upon this or- 

 ganization. I must here ask if these animals have 

 not been confounded with the sexless larvie which 

 multiply by fissm-ation like those of Medusae. 



3 Coition has often been observed with Planaria 

 and Mesostoynum, and has been figured by Baer, 

 Dugis, and Focke. 



* [ § 128, note 1.] See Leidy (loc. cit.) ; he this subdivision could not be carried successfully 

 found that with P/tagocata (Planaria) gracilis, beyond three or foui- parts. — Ed. 



