20 ILLINOIS BIOLOGICAL MONOGRAPHS [238 



Cyclocoela Dujardin (1845) and in view of this fact calls attention to the 

 recommendation of the International Zoological Commission in the Inter- 

 national Code which reads: — "It is well to avoid the introduction of new 

 generic names which differ from generic names already in use only in ter- 

 mination or in a slight variation in spelling which might lead to confusion. 

 But once introduced, such names are not to be rejected on this account." 



Structure of the Genus 



The description of Stossich (1902) states that these worms are covered 

 with spines which that author interprets of sufficient importance to be a 

 specific characteristic. Although Zeder (1803) observed these granula- 

 tions he was not able to determine their real nature and suggests that they 

 are either cellular structures or glands underlying the thin cuticula. It 

 was not until the work of Fuhrmann (1904) was published that the true 

 nature of these, which are really pits became known. This author de- 

 scribed and figured these pits as found on the ventral surface of Bothrio- 

 gaster variolaris and stated that he has observed similar depressions on 

 both the dorsum and venter of Cyclocoelutn mutabile. However, he raises 

 the question whether these are not a product of preservation. Kossack 

 (1911) verified the work of Fuhrmann by similar observations on several 

 species belonging to at least three distinct genera of this family. He sup- 

 ported the view of Fuhrmann as to their origin and added as evidence of 

 their nonexistence in living material that the authors who had opportunity 

 to study living material — notably von Siebold and Van Beneden — did not 

 mention their presence. 



There can be no doubt that Zeder (1800, probably also 1803) made 

 observations on living material. That the particular observation men- 

 tioned above was made from living material of course is only a matter of 

 conjecture. It is evident, however, that at least one author who studied 

 living material did observe these pits. Hence the lack of mention by von 

 Siebold and Van Beneden is not sufficient evidence to prove their non- 

 existence in living material. 



That the state of contraction at the time of fixation is responsible for 

 the degree of depth and apparent frequency of these pits remains unques- 

 tioned. But unless they occur in the living specimen it would be impos- 

 sible to find them so regularly in preserved material. In addition if they 

 are artifacts of preservation one would expect to find them in other trema- 

 tides of similar size and structure. 



While the writer has not had opportunity to study living Cyclocoelidae 

 he has found the above mentioned "Grubchen" of Kossack, the "ovale 

 depressionen" of Fuhrmann, constantly in more than one hundred and 

 fifty specimens belonging to at least nine species of the genus Cyclocoelum 

 and in Haematotrephus similis. While in the study of more than a hundred 



