270 CHAKLES HOWARD EDMONDSON 



less rapidly. Nelson ('18) found that the rotary movement of 

 the crystalline style in Modiolus was not continuous during diges- 

 tion, but was inhibited at intervals, periods of rest alternating 

 with periods of activity. Repeated attempts to verify the 

 rotary movements of the crystalline style in Mya have so far been 

 without success on my part, but from observations on the de- 

 velopment of the organ, as presented later in this paper, one may 

 safely conclude that rotation occurs. 



By comparing the lengths of the crystalline styles in a large 

 number of individuals with the shells, one finds that the style of 

 Mya arenaria averages approximately 72 per cent of the length 

 of the shell. In a specimen with a shell length of 120 mm. the 

 crystalline style usually measures from 85 to 90 mm. In diame- 

 ter the style of a medium-sized specimen of Mya is approximately 

 3 mm. at the larger extremity. The style is firm, quite solid, 

 and translucent in a fresh specimen, but lacks the luster so 

 characteristic of the same organ in Schizothaerus nuttallii and 

 Macoma nasuta. 



Cross-sections of the crystalline style of Mya arenaria reveal 

 the concentric layers in the substance of the organ (fig. 5). I 

 have been able to count from eighty to one hundred of such 

 layers, which vary considerably in thickness. 



At irregular intervals between the concentric layers of the crys- 

 talline style of Mya arenaria I have been able to make out 

 minute, epindle-shaped areas which have the morphological ap- 

 pearance and the staining reaction of mucus. These are repre- 

 sented in a portion of a longitudinal section under high magnifica- 

 tion (fig. 6). I have at no time observed a central core of food 

 matter in a mature crystalline style of Mya arenaria. 



4. THE RELATION OF THE CRYSTALLINE STYLE TO THE INTESTINAL 

 TRACT IN MYA ARENARIA, AND FEATURES OF THE STYLE SAC 



In Mya arenaria, for a distance of from 10 to 15 mm. from the 

 floor of the stomach, the style sac and the proximal extremity of 

 the intestine are incompletely separated (figs. 1 and 17). Cross- 

 sections through the style sac and intestine just below the floor 

 of the stomach show the union between the two tubes, in all es- 



