408 071 the Anatorny and Histology of Nemer tines. 



Annelids — though in them only, and not in the Turbellaria, 

 would it be possible to discover them. I will merely draw 

 attention to the fact that with the appearance of this second 

 pair we find that a lateral line appears in the Nemertines as 

 the bearer of sense-organs, precisely as we find it in the 

 Annelids. 



The genital products are either formed directly in the 

 parenchyma, in which case a membrane forms round them, 

 constituting a sac, or else they arise in the walls of sacs which 

 alternate with the intestinal cffica. Before maturity is reached 

 a duct is formed, one from each sac. In the non-metanie- 

 rized forms the first of these methods appears to prevail 

 ( Carinella)^ in the metamerized forms the latter [Cerehratalus^ 

 JDrepanoplwrus) . Moreover in these forms, as in Prosadeno- 

 poruSj Geoiiemertes, and many others, several genital sacs are 

 situated between a single pair of intestinal cseca, and we con- 

 sequently find several genital pores in one metamere. 

 Nemertines are not all of separate sexes : the terrestrial and 

 allied forms, e. y. the Prosadenoporids, are hermaphrodite. 

 Hermaphrodite forms are also found among the Tetra- 

 stemmids, which are closely allied to the Prosadenoporids. 

 JProsorhockmus and Mo7io2)ora are stated to be viviparous. 



The extraordinarily complicated genital organs of the 

 Turbellaria exclude any comparison with those of Nemer- 

 tines. 



But even as regards the genital organs of the Polychajte 

 Annelids, it is only in their simplicity that those of the 

 Nemertines agree. 



Shortly stated, the conclusion we deduce from the con- 

 siderations which we have discussed in the above pages 

 amounts to this : — That in many respects the organization of 

 Nemertines exhibits an affinity with that of the Turbellaria, 

 but that on the whole this is put into the shade by the genei-al 

 Annelid-like structure of the animals which we have been 

 considering. 



If we merely observe the living flat Nemertine crawling 

 in its mucus, and compare it with a Polycha^te or an Oligo- 

 chsete, the metamerism of which is exhibited externally by 

 means of rings and the arrangement of bundles of setse, we 

 find but little difliculty in persuading ourselves to follow our 

 predecessors in the field of natural history and in agreeing 

 with the place they assigned to these worms in their classifi- 

 cations — so long, that is, as we are compelled to work with 

 the same appliances as they had. To-day, however, when 

 methods and micioseupy have overcome uiituld ditiieulties 



