236 MARTIN F. WOODWARD. 



Thus we find in both forms similarly placed lateral and 

 ventral protractors among the extrinsic muscles, while 

 among the intrinsic the dorsal, ventral longitudinal muscles 

 connected with the infra-radular membrane are similar, as 

 also is the transverse ventral muscle. The remaining 

 muscles, however, diifer, as, moreover, do the cartilages, 

 since there are three pairs of cartilages in Patella and only 

 two pairs in Pieurotomaria. 



The Crop. — As in most Diotocardia, the first portion of the 

 oesophagus is much dilated and saccular, and may be thus 

 spoken of as a crop. It is closely connected with the body-wall 

 by fine bundles of muscle-fibres, making the removal of the 

 latter very difficult, and giving the crop a villous appearance. 

 Its intei'nal structure also is very characteristic, its walls, as 

 in Haliotis, being thickly covered by numerous papillee 

 (figs. 9 and 10). These papillae are, however, wanting in 

 front where the crop and buccal cavity join, and in the 

 morphological dorsal and ventral middle line. The epithelium 

 covering these papillse is highly glandulai', and the centre of 

 each papilla is a blood-lacuna. The presence of the papillae 

 thus causes an increase of the seci-etory epithelium. 



Situated immediately behind the odontophore is a somewhat 

 oval thickening. At a little distance from this structure we 

 find on either side a slit-like depression (fig. 10, If. Ip^.), 

 which we may term the lateral oesophageal pouch. Each of 

 these depressions is bounded by a couple of folds (lettered in 

 fig. 10, 1 and 2 on the left side, and 3 and 4 on the right). 

 Tracing these structures back, we find that by their enlarge- 

 ment and rotation they cause the crop to assume a very 

 complicated form. Thus the two ventral folds 2 and 3, 

 enclosing between them the ventral median area, pass first to 

 the right side and then gradually ascend until they assume a 

 dorsal position ; this causes a corresponding displacement of 

 the two dorsal folds (1 and 4), which pass down the left side 

 until they attain a ventral position. At the same time the 

 lateral pouches become enlarged, and undergo a corresponding 

 displacement; thus the original left pouch (/jj.) now constitutes 



