248 SUMMARY OP CURRENT RESEARCHES RELATING TO 



refers to Lis already published suggestion tliat the Triclads wore 

 derived from the Polyclads by a reduction in the number of tho 

 enteric branches, testes, and ovaries, by a conversion of part of tho 

 ovary into yolk-glands, by a reduction of the lateral parts of the body, 

 the loss of the primary entcron, and the greater development of 

 bilateral symmetry. The detection of a water-vascular system in 

 the Polyclads has diminished the gap between tho two groups. 

 Difficulties are presented to us by the cenogenotic modes of develop- 

 ment which are so marked in Triclads. 



"With regard to tho relationship of the Turbellaria to tho Tre- 

 matoda, Lang's studies, confirmed by those of Gaffron on the nervous 

 system, show that the relationship is closer than has been generally 

 supposed. It is probable that the Trematodes arose from Triclads in 

 which the mouth had already taken up an anterior position ; the two 

 oral suckers of Tristomida have a close resemblance to the marginal 

 tentacles of certain Triclads, and their ventral sucker to that which is 

 found in some members of the more primitive group. 



Lang agrees with Hallez and GratF in thinking that tho Triclads 

 are closely allied to the AUoiocoela among the Khabdoccelida ; only, 

 in exact opposition to Graflf and Brauu, he thinks that the AUoiocoela 

 arose from the Triclads. 



The difficult question of the position of the Acoela is glanced at ; 

 as to the Nemertinoa, the author expresses the opinion that it is im- 

 possible to compare their organs directly with those of the Turbellaria. 



The last problem discussed is that of the morphology of the 

 excretory organs of worms and their relation to the view that the 

 Platyhelmintbs owe their origin to being degenerated from higher 

 segmented worms. Against the view that the large open intercellular 

 infundibula of Annelids are homologous with the excretory cells of 

 the Platyhelminth kidney and that of the larva of Annelids, and in 

 support of the doctrine that they are neomorphs, he refers to recent 

 observations by Meyer on the development of Terehella ; in this annelid 

 the ciliated infundibulum is seen to be formed from a group of cells 

 which are primitively completely separated from the rudimentary 

 excretory organ, and only come secondarily into connection with it. 



New Turbellarian.* — This was discovered living on Nehalia by 

 M. Ecpiachoff. From his preliminary note the animal appears to be 

 elongated in form, and ciliated mainly on the tapering, proboscidiform 

 anterior extremity, which is marked off by a circular groove. Another 

 groove, situated ventrally, forms a kind of sole, with a further median 

 furrow subdividing that surface. The anterior extremity is so termed 

 because it is to the front when the animal moves. It is at the 

 posterior extremity, according to this nomenclature, that the pharynx 

 and copulatory organs occur. The intestine runs through two-thii-ds 

 of the body, and is coiled or straight according as the generative 

 organs are little or well developed. The generative organs are paired 

 throughout. The female organs (ovary and yolk-forming bodies) lie 

 round the pharynx, whereas the round testes are found on either side 



* Zool. Anzcig., vii. (1884) pp. 717-9. 



