JELLY-FISHES. 99 



has for a function the support of the axis in the water. In Agalma, however, it 

 is so small that its functional importance in this respect is very slight. The axis 

 of the Agalma is divided into two regions, one of which lies adjacent to the float, 

 and is called the nectostem, and the other, more distant from the same, the polyp- 

 stem. In larger specimens the length of the nectostem is about one-third that of 

 the polypstem. The former bears a number of appendages of interesting char- 

 acter called the nectocalices. These bodies are situated in two rows or series, and 

 are glassy clear in their transparency. Their union with the stem is of a very fragile 

 nature, and easily ruptured when the animal is raised out of the water. If we examine 

 a single nectocalyx we shall find that it resembles closely a medusa bell (hydroid 

 gonophore) in which the walls have a more or less polygonal shape. This form is the 

 result of a flattening of two opposite sides of the nectocalyx in order that it may fit 

 closely in the series of which it is a member. Each nectocalyx has a cavity within, 

 which opens into the surrounding water through a circular orifice, partly closed by a 

 thin, washer-shaped body called the veil. The apex of the nectocalyx is situated 

 oi^posite the external opening, and marks the point of union of the bell and the necto- 

 stem. On either side of the apex, embracing the nectostem, the bell walls are con- 

 tinued into gelatinous horns which closely interlock with similar projections from 

 nectocalices situated in the opposite series. 



The arrangement of the nectocalices on the nectostem is as follows : There are two 

 rows or series of these bodies placed diametrically opposite each other on the axis. 

 Each series is composed of a number of nectocalices placed one above the other, fitting 

 closely together by the flat faces on the outside of these bodies. The gelatinous horns 

 already mentioned interlock with corresponding bodies from the opposite series. By 

 the close approximation of adjacent bells on their flat faces, and the interlocking of 

 bells from opposite series, a certain rigidity is given to this portion of the animal, 

 notwithstanding the delicate attachment to the stem. 



The disposition of the nectocalices causes all the bell openings in each series to 

 point in the same direction, or almost at right angles to the length of the axis. The 

 action of the nectocalices is as follows : They are, as their name implies, structures 

 for a propulsion of the Agalma from place to place through the water. When water 

 is taken into their bell cavities, by a violent contraction of the bell walls it is violently 

 forced out through the opening into that cavity against the surrounding water in 

 which the medusa is floating. The necessary result of this action is that the animal 

 is forced through the water in an opposite direction from that in which the resistance 

 takes place. By a nice adjustment of the different bells, acting in concert or indeiDend- 

 ently, almost any motion in any direction can be imparted to the Agalma. Just 

 below the float on the nectostem there is a small cluster of minute buds in which can 

 be found nectocalices of all sizes and in all conditions of growth. 



The attachment of the nectocalyx or swimming bell to the nectostem, not only 

 serves to move the animal from place to place, but also renders it possible for the 

 swimming bell to receive its nourishment. Although the nectocalyx resembles very 

 closely a medusa, it is a medusa bell without a mouth or stomach. It is not capable 

 of capturing nourishment for itself, but is dependant upon others for that purpose. 

 The nectocalyx has a system of tubes on its inner bell walls which communicate with 

 the cavity of the nectostem by means of a small vessel which lies in the peduncle by 

 which it is attached. Through this system of tubes the nutritive fluid is supplied to 

 the nectocalyx from a common receptacle, the cavity of the stem. In the largest 



