1 882.] The Siphonophores. 95 



radial tubes as well as the point of attachment of the bell to the 

 stem, shows that one side of the bell is not abnormally developed 

 at the expense of the other. Its general form is exactly what 

 would take place if an Agalma bell were much elongated in the 

 line of its height, in order to secure a greater capacity for the 



The most important variation in shape from the anterior bell, 

 is the formation of two ridges extending the whole length of 

 the under side of the posterior nectocalyx on the side which is 

 opposite that part of the anterior bell which is thickened and 

 bears the somatocyst. These ridges are continued into two 

 prominences beyond the bell opening. 1 In the interval between 

 these two ridges there is a groove in which is lodged the stem 

 when retracted. In some genera, as Abyla, still further means of 

 covering the stem when thus retracted are found, but in Diphyes 

 the groove is without covering. The posterior bell is smaller 

 than the anterior, and is easily detached. Its radial system of 

 vessels communicates with the stem cavity by a small vessel 

 which is destitute of mantel tubes or somatocyst. While the two 

 nectocalyces of Diphyes are the most prominent structures in the 

 animal when alive, and the only organs to be studied in alcoholic 

 specimens, they are by no means the most- important. The 

 active habits of Diphyes has given them this predominance in 

 -size. There remain many other appendages to the stem yet to 

 be mentioned. 



These parts of the colony are fastened regularly along the 

 whole length of the stem to its very extremity. They consist of 

 covering-scales, polypites to which are appended tentacles dotted 

 along their length with tentacular pendants, and clusters of sex- 

 ual bells. Representatives of the bodies called tasters in my 

 account of Agalma do not exist, as far as known, in the Diphyidas. 

 The appendages are not placed irregularly upon the stem, a 

 Polypite in one place and a cluster of sexual bells in another, but 

 are found in clusters, separated by short intervals of the stem. 



Each « 



ists of a covering-scale, a polypit 



hahly act as rudders to determine the d 



