60 THURLOW C. NELSON 



shield, which forms a sort of valve over the orifice. During the 

 winter this reserve serves to nourish the animal. His conclusions 

 are based on a study of two closely related fresh-water forms. 



The presence of such a reserve of nutriment in the intestine 

 was held by Krunkenberg ('86) to be untenable. 



The inaugural thesis of Haseloff ('88) is the most extensive 

 single work on the crystalline style. He studied seven different 

 forms, but based his conclusions largely upon Mytilus. After 

 describing the general anatomical relations of the style, the 

 author cites experiments in which Mytili were kept in filtered 

 and in normal sea-water. Finding that the style grew thinner 

 and finally disappeared in those aniuials which were starved, 

 he concluded that it must be a reserve of nutriment. 



Haseloff was not aware of the work of Hazay until after he 

 had finished his investigations. From his own results and those 

 of Hazay, he concluded that the style was a structure built up 

 in time of excess nutrition and absorbed in times of want. As 

 for its origin, he believed it to be a chemical transformation of 

 surplus nutriment, and not an epithelial secretion. Chemical 

 tests applied by him showed the style to be albuminous in 

 nature. He concluded that the presence of the style is almost 

 universal in the lamellibranchs. 



Dubois ('92) thought that the style serves as nutriment for 

 parasites useful to their host. 



Stempell ('98) believed the style to be lacking in the Nuculidae. 

 The large gastric shield which he found in these forms was held 

 to be a reserve material, absorbed by the gastric epithelium and 

 used in the development of the sexual organs. 



List ('02) in his beautiful monograph of Mytilus, gives a most 

 comprehensive treatment of the subject. The historical sum- 

 mary is fairly complete and accurate, save that he does not give 

 proper credit to some former workers. His investigations 

 cover the anatomical, histological, and certain physiological 

 aspects of the problem. He was the first to study the formation 

 of the style in- the living animal, and found that color particles 

 taken up by the mussels in feeding were built up into the body 

 of the style. 



