240 THE AMERICAN MUSEUM JOURNAL 



(the so-called "glass" sponges), or their skeletons may be partly 

 or entirely made up of a network of spongin fibers. A few 

 sponges^have no skeletons at all. 



Those sponges which have six-rayed spicules belong to the 

 order Hexactinellida, a group marked by forms of unusual beauty 

 and grace, of which a fine collection is shown in this alcove. In 

 some of these (suborder Lissacina), the spicules are independent 

 during growth and are felted together by means of their hooks 

 and spines; in others (suborder Dictyonina), the overlapping 

 ends of the spicules have grown together to form a rigid lattice- 

 like framework. 



Suborder Lissacina. — The several species of Euplectella 

 (Venus's Flower-basket) are especially noticeable for delicate 

 beauty, while Walteria is remarkable for its odd tree-like form. 

 Acanthascus, Rhahdocalyptus and Crateromorpha are also repre- 

 sented by fine specimens, (see opposite page) and give a good 

 idea of the variety of forms which these sponges may assume, 

 while the remarkable vase-like Hyalascus similis Ijima (Fig. i8, 

 p. 239) is not only the type of its species, but is the only specimen 

 known to have been foimd. 



The so-called "glass-rope" sponges (Hyalonema) are re- 

 markable for the twisted, cylindrical bundle of elongated spicules 

 projecting from the lower end. In life this stalk-like support is 

 anchored in the mud at the sea-bottom by means of barbs and 

 hooks at the lower end of the spicules. An interesting peculiarity 

 of this sponge is its association with tiny Zoophytes (Palythoa) 

 which are always found growing upon its stem (see Fig. 22). 

 This is an illustration of the phenomenon of symbiosis, indicating 

 an association of two animal forms for their mutual advantage. 



Suborder Dictyonina. — The two specimens of Farrea occa 

 Carter (see Fig. 14, p. 230) and Aphrocallistes show particularly 

 w'ell the lattice-like framework peculiar to this group, and also 

 the characteristic manner of growth of these sponges. 



The glass sponges are all imiversally distributed in the deep 

 waters of tropical seas. ^lost of the specimens exhibited in this 

 Museum were collected in the Sagami Sea, an arm of the Sea of 

 Japan. This is a particularly favorable locality, as the sea- 

 bottom falls away rapidly to a great depth close to the shore, 



[26] 



