12 HISTORICAL REVIEW. 



In 1876 von Graff subjected (liuttodcrmn nilidulum to an examination, 

 which considering the amount of material and the methods then in vogue, was 

 more than onhnarily searching; and while he, like Tullherg, fell into error 

 regarding the urogenital organs, his results relating to the other systems, espe- 

 cially the nervous, were of the greatest inijiortance. While not entirely com- 

 mitted to any particular belief regarding the animal's relationships he was 

 inclined to uphold Keferstein, Diesing, and others; and j'et he drew attention 

 to the fact that the spicules, gills, mode of egg development, and musculature 

 are so unique that the genus may in reality belong elsewhere, possibly in close 

 proximity to the Turbellaria owing to the close correspondence in the nervous 

 systems. 



In 1877 and the following year von Ihering proposed a new classification 

 of the Mollusca based on extensive anatomical researches largely concerned with 

 the nervous system. He drew attention to the very important fact, not pre- 

 viously recognized, that in many fundamental respects the Solenogastres are 

 allied to the Chitons. In his opinion the ancestral neomenian was probably 

 not distantly related to the gephyreans or nemerteans and accordingly lacked 

 a true shell, and Chitonellus, with its small shell and extensive girdle, is thus 

 more closely related to the Solenogastres than other Chitons and must there- 

 fore be looked upon as a connecting link. Owing to the presence of lateral 

 nerves the Chitons, Chitonellus, and the Solenogastres are clearly differen- 

 tiated from the gephyrean worms and annelids, so that in this and other respects 

 they approach the molluscs. On this account a new phylum of Vermes, the 

 Amphineura, was created for their reception. The following year ('78) this 

 same author reviewed the work of TuUberg, Koren and Daniellssen, and von 

 Graff in a suggestive paper, and was more strongly convinced than before that 

 his conclusions were justified. These papers of von Ihering's created much 

 criticism, some of it decidedly hostile, but it is undoubtedly true that, while 

 some of the results have not proved to be correct, the work as a whole had a 

 stimulating effect and has been productive of much good. 



During this same period ('77) Koren and Daniellssen described a number 

 of species collected along the Scandinavian peninsula. In most cases the 

 descriJDtions are so brief that they are not even of generic value, and the animals 

 remain practically unknown down to the present day. Ncomenia carinata 

 {Solenopus nitidulus) is described at some length, but the facts adduced are 

 not strikingly different from those presented by Tullberg. By these authors 

 the Solenogastres were considered to be true molluscs, and were placed among 

 the opisthobranchs in a new order, Telobranchiata. 



