110 STROPHOMKNIA SCANDENS. 



CorrelaU'd with (he jjosterior attachment of the pliarynx is the excessive 

 devclopiHcnt of the anterior coecum (Plate 12, fig. 1), that extends forward to 

 file hiniler limits of the atrial cavity. In one specimen its walls are lined 

 tlii-o\ighout with pyriform digestive cells, whose clear basal portion holds a 

 small compact nucleus while the vacuolated distal part contains numerous 

 granules characteristic of this type of cell. In another individual treated in 

 precisely the same way the granular jiortion of the cells was absent as was the 

 case in other parts of the digestive tract. As was noted in the case of P. hawaii- 

 ensis this appears to be the normal method of ridding the cells of their secretion. 

 In the hinder jiortions of the coecum gut pouches appear and becoming more 

 fully developed a short distance more posteriorly they continue with much 

 regularity to the region of the heart where they abruptly disappear. Beneath 

 the anterior end of the pericardium the intestine continues as a tube of relatively 

 large calibre, but at the posterior end it rapidly narrows down to open into the 

 cloaca (see Plate 12). 



As is represented (Plate 13, fig. 2, and Plate 16), the pericardium of this 

 species is of considerable size and contains in addition to the heart a number 

 of mature ova. Histologically the differentiation of auricle and ventricle is not 

 clearly marked and save for a constriction there is nothing to distinguish these 

 two divisions. The blood occupying the interstices between all the organs in 

 the posterior part of the body passes into the auricle by a wide opening and thence 

 pours into the ventricle through an aperture not guarded by clearly defined 

 valves. From the forward end of the heart the aorta takes its rise and with 

 the usual position makes its way to the head after having supplied the gonad. 

 The lilood spaces at the anterior end of the body are very limited, more so in 

 fact than is indicated in the figures which have omitted the intrinsic muscles of 

 the digestive tract as well as retractors and protractors that attach to the body 

 wall. However, the course that the blood takes in passing through the body 

 projier differs in no essential particular from that of P. hawaiiensis. 



The corpuscles are spindle shaped (Plate 36, fig. 12) and the small densely 

 staining nucleus is superficially placed, in some cases being elevated above the 

 surface of the slightly yellowish homogeneous cytoplasm. 



In a preceding paper (Heath '04) attention has been called to the fact that 

 in its more important details, especially in the relations of the labio-buccal sys- 

 tem, the nervous system of this species shows a striking similarity to the Chitons 

 and certain prosobranchs. The brain is relatively small and holds the usual 

 position on the dorsal side of the jiharynx behind the mouth cavity. As usual 



