PRONEOMENIA HAWAIIENSIS. 85 



encircles the atrial cavity. The epithelial cells bounding these ridges (Mund- 

 leisten) are columnar, richly ciliated and besides the centrally placed spherical 

 nucleus contain a small quantity of greenish yellow pigment. Within the 

 ridges are a few connective and muscle elements and an occasional nerve fibre, 

 all loosely arranged and permitting the entrance of multitudes of blood cor- 

 puscles that probably cause the distension of these organs. 



The area bounded by these two sensory prominences is the cirrose region 

 characterized by the presence of numbers of hollow finger-shaped projections 

 each attached by its base and extending into the atrial cavity. The cells com- 

 posing these organs differ to some extent in different specimens but agree in 

 being low, non-ciliated, and charged with a considerable ciuantity of the usual 

 greenish yellow pigment and a varying amount of some hyaline secretion that 

 often covers their external surface. More slender elements, scant in numbers, 

 occur among these ordinary cells; they may be sensory but some at least appear 

 to be cells from which the secretion has recently been discharged. The cavity 

 within each cirrus is usually very slender and is traversed by a muscle and nerve 

 fibre. In very exceptional cases there are one or two blood corpuscles; but 

 neither in this nor in other species of Solenogastres have I found any indication 

 that these play an important part in the process of respiration. Beneath the 

 cirri is a felt-work of muscle, connective and nerve fibres together with blood 

 corpuscles and leucocytes beyond which is a mass of ganglion cells connected with 

 the central nervous system and on the other hand with sense organs of the 

 atrium and probably of the hypodermis. 



A very short distance within the inner ridge the digestive tract narrows 

 rather abruptly, the character of the epithelial lining changes radically, and 

 since it marks the point of entrance of the dorsal salivary gland it may be con- 

 sidered the line separating the mouth and pharynx. According to such an in- 

 terpretation the pharyngeal wall, lined with a relatively heavy cuticle, is thrown 

 into a series of ridges that course more or less longitudinallj^ throughout its entire 

 extent. In the majority of cases the cells are high, with central oval nucleus 

 and a slight .secretion that had escaped at various points through some of the 

 exceedingly minute pores passing through the lining cuticle. 



The so-called dorsal, or accessory, sahvary gland is attached to the dorsal 

 wall of the pharynx immediately behind the brain (Plate 5, fig. 2). The cells 

 composing it are one layer thick, and as the duct itself is short and unbranched 

 the gland is necessarily compact and globular in form. The epithelial lining of 

 the pharynx is continued inward to form the lining of the duct between whose 



