792 
THE VOYAGE OF H.M.S. CHALLENGER. 
the wide differences which separate it as a member of the Hydrozoa from the Actinozoa. 
In a dredging off the mouth of the Rio de la Plata in 600 fathoms, six genera of the 
family Stylasteridse, which, together with the Milleporidse, form the group Hydro- 
corallinae, were brought up at once in good condition, and all but one with fully developed 
generative organs. An examination of this material soon showed that the Stylasteridse, 
which had until then been placed amongst the Oculinidse, are, like the Milleporidse, 
Hydroids. In all of them there is an elaborate system of division of labour amongst the 
members composing the colonies. Some devoid of stomach catch the food and hand it to 
Fig. 27 6. — Cryptohelia pudica, M.-Edw. and Haime ; twice tlie natural size. 
others, the sole function of which is digestion for the general good, others again are gene- 
rative zooids. The accompanying figure shows a stem of one these corals, Cryptohelia 
pudica, so called because, as will be seen in the drawing (fig. 276), it has a shield or lid in 
front of each of the cups in which the polyps live concealed. The mouths of the cups 
are all turned to one face of the stock. Each of the small cups is notched all round its 
margin, and in each notch is a grasping zooid (dactylozooid), /whilst in the centre of each 
ring of dactylozooids is a stomachzooid or gastrozooid which digests the food and 
distributes the products all over the colony by means of an elaborate system of canals. 
The generative or nursezooids lie embedded in the walls of the cups. In some Stylasteridse 
the division of labour is even more complex than here. 
