202 HYATT, 



valve, and antero-posterior from the lopliophore to the end 

 of the gastric coecum. 



Oesophagus. The proportion of antero-posterior di- 

 ameter to the length of the stomach from the oesophageal 

 valve to the end of the coecum, varied but little from ^ in 

 each genus. But the next character, the proportions of 

 its own antero-posterior to its own dorso-ventral diameter, 

 show a determinate and steady decrement in its length. 



Stomach. The proportions of the dorso-ventral to the 

 antero-posterior diameter determine the fact stated above 

 with regard to the increase in the size of the canal to Pec- 

 tinatella, and its decrease or fluctuation in Cristatella. In 

 addition to the decrement in the length of the oesophagus, 

 there is also a decrement in the ventro-dorsal from what 

 it is in Pectinatella, ^ of the antero-posterior, to only ^ the 

 latter, very nearly the same proportions it had originally 

 in Fredericella. The next proportion, however, shows a 

 curious fact. Although there is this decrease in ventro- 

 dorsal diameter there is an increment in the dextro-sinis- 

 tral diameter; or, in other words, the stomach retains in 

 Cristatella the great breadth of the dextro-sinistral diam- 

 eter, which it attained in Pectinatella : while, on the other 

 hand, it loses the increment of the ventro-dorsal diameter. 

 This explains the greater breadth of the alimentary canal, 

 when seen from the dorsal side in Cristatella, as compared 

 with its narrow look when viewed laterally. 



Intestine. Only one series of measurements was made 

 of the intestine, ventro-dor sally near the phyloric valve, 

 and antero-posteriorly from the valve to the anus. The 

 proportions of these two diameters appeared to be invari- 

 able ; but, nevertheless, the absolute size of the intestine 

 is greater in Plumatella and in Pectinatella, than in any 

 other genus. In Cristatella, like the stomach, it became 

 « — when seen from the side — very narrow, but is of Pec- 

 tinatellean proportions when seen in front or dorsally. 



RETRACTORS. 



(Esophageal Betr actors. The characteristics preceding 

 the proportional breadth of this branch of the retractors 



