100 DORYMENIA ACUTA. 



The matrix cells of the radula are comparatively small and the teeth 

 numerous so that an accurate determination of the development of the teeth and 

 basement membrane is difficult. Odontoblasts, holding the ordinary position 

 and with the usual appearance are present and numerous enamel cells arise from 

 the bottom of the radular sac. These latter elements may be traced forward a 

 short distance among the newlj' developed teeth where they disappear. The 

 cells responsible for the formation of the basement membrane are not unlike 

 the odontoblasts all of which blend with the epithelial cells of the ventral side 

 of the radular sac. In all essential respects therefore the development of the 

 radula in this species is not unlike what exists in Limifossor talpoideus. 



Immediatelj' behind the opening of the pharynx into the intestine the walls 

 of the latter develop a circular fold (Plate 15, fig. 7) which in life may be less 

 contracted and serve as a valve. Anterior to it the intestinal coecum extends 

 as far forward as the brain. It is almost wholly devoid of diverticula, though 

 its low epithelial lining is thrown into numerous small folds on its ventral surface. 

 Slightly behind the valve-like fold just mentioned the intestine proper arises, 

 characterized by diverticula of almost mathematical regularity lined by the 

 usual high club-shaped digestive cells, except underneath the gonad where the 

 intestinal epithelium loses its glandular character and its low columnar cells 

 support a coat of cilia. This state of affairs continues to the front end of the 

 coelomoducts where the canal rapidly decreases in diameter and becomes ciliated 

 throughout. Making its way to the dorsal side of the animal it passes between 

 the pericardium and gonoduct to open into the cloacal chamber. 



The pericardial cavity is a comparatively large space whose general shape 

 and relations may be determined from Plate 6, fig. 4. The cells composing its 

 epithelial lining are indistinct in outline, yet, judging from the nuclei, are more 

 numerous than in any other species of Solenogastre described in the present 

 paper. The heart also is of large size (Plate 15, figs. 4, 6) in both specimens which 

 were sectioned, and very clearly consists of an auricle and ventricle. The first 

 named division is much distended and the walls are thin and delicate, consisting 

 externally of an epithehal sheet resembling that lining the pericardium, internally 

 supported by a few muscle fibres. These form a loose meshwork from which 

 occasional fibres pass across the auricular cavity to be inserted elsewhere in the 

 wall. The long, sharply defined median dorsal sinus, extending from the pos- 

 terior end of the bodj-, enlarges as it passes forward and enters the auricle on its 

 posterior border. As usual the ventricular walls are of greater thickness and the 

 spaces formed bj- the interlacing fibres relatively small and filled with groups 



