-2- 

 with other f orms . In chitons only pallial margin is supplied with characteristic a»*M?eS3j 

 cuticular layer and spine structures on its dorsal and also on its ventral surface.This 

 pallial margin is furnlshed with a speci^al musculature. The observations of 

 Chitonellus show that by smallest expansion of Shell parts and of foot this pallial 

 margin together with its musculature obtains relatively much bigger size. Presence 

 of the same integuraent tissue (Texture) not only at pallial aargin but also between 

 succesive shell parts could point out to_the thought that this characteristic 

 integument formation was originally expended over the whole back surface, which in 

 Chton is supressed by shell parts thrust upon each other and is again noticeable in 

 Chitonellus because oifi the reduction of shell parts . The forming of foot in Chitonellus 

 in the posterior part of body is much more powerful. Anteriorly the foot gets to be 

 considerably smallerj since the gills are absent in anterior part of body, pallial 

 cavity (gill cavity) appears there only as a piain and only slightly expanded forrow 

 with only an indication of foot and no gill formation. Also the forming of the head is to 

 be rudimanfcary . 



Frorn these situations are derivable only those Neomenia which are 

 characteristic by complete absence of foot and by restriction of gill cavity to 

 posterior part, which seems to be here deposited as cloaca and continues anteriorly 

 only in form of a ventral groove.In addition the Involution of the abdominal groove 

 in Chaetoderma is grown.( Jünrthe abdominal groove is recently denied by Hansen). 

 Here it is only cloace with its gills as the remains of original pallial cavity. 



In Neomenia as also in Chaetoderma the characteristic integument formation 

 Stretches over the whole circumference of the body and also body's musculature^f 

 which shows the conditions oÄ a cuticolomuscular tube- is to a larger degree traced back 



to musculature of pallial margin. All these conditions are understandable if we procced 

 with the compar6sson from Chiton to Chitonellus, than Neomenia and finally Cheatoderma. 

 The latter are considered, as mentioned, as involute or metamorphorized forras. To the 



reastns which already Pelseneer cited, » the most important: in Chiton the even 





