56 THURLOW C. NELSON 



three more loops in the visceral mass passes to the rectum and 

 anus. 



The first portion of the intestine (the 'Magendarm' of the 

 Germans) which lies between the stomach and the sharp bend 

 beneath the heart, consists essentially of two regions. On the 

 right side is the intestine proper and on the left the groove which 

 lodges the style. Since this groove or tube is open at both ends, 

 in the type under consideration, I shall refer to it as the style 

 sac, rather than as the style caecum, as it is commonly called. 



Incompletely separating the intestine and style sac are a dor- 

 sal and a ventral ridge, forming two ' typhlosoles' which extend 

 throughout this portion of the intestine. The broad surfaces of 

 these ridges are in apposition, leaving a narrow slit through which 

 the style sac and intestine are in communication throughout their 

 extent. The relation between these structures is better under- 

 stood from figure 2, a transverse section through this portion of 

 the alimentary tract. 



The style itself, when fully formed, completely fills the lumen 

 in which it lies. It tapers gradually from before backwards, 

 becoming a more tenuous thread at the posterior end of the 

 style sac. The anterior end projects from the pylorus across the 

 cavity of the stomach to the opposite wall. 



At the point of contact between the head of the style and the 

 gastric mucosa there is developed a plate-like structure of car- 

 tilaginous consistency. It conforms to the outline of the stomach 

 wall at that point, and may bear an apical projection near its 

 center. In some forms (Pholas, Donax, Martesia) this car- 

 tilaginous sheet lines the whole of the stomach cavity. As this 

 structure has not, to my knowledge, been described by English 

 or American investigators, I propose the name 'gastric shield.' 



To avoid any misunderstanding, there is introduced here a 

 synonomy of terms used by the earlier investigators. The 

 crystalline style of English-speaking scientists is the 'stylet 

 cristallin,' of Barrois ('89), 'tige hyalin,' of Siebold ('48), 'tige 

 cristalline,' of Coupin ('00), the 'Diinndarmkorper' of Hazay 

 ('81), and the 'stylus cristallinus' of its discoverer, Anton de 

 Heide (1686). 



