4 BULLETIN OF THE BUREAU OF FISHERIES. 



a few large, smooth, and slightly curved styles project, forming a well-marked tuft. These styles 

 measure 4oo-i6o(( long, 8-10/1 wide. The longest styles lie nearest the apex of the column and some 

 of them project beyond the surface of the sponge. Mingled with the mature styles are younger 

 spicules of the same type, but slenderer and shorter. Projecting from the sides of some of the larger 

 homy columns are a few small styles, 80 by 5-6/1, some of them distinctly spinose, others with few and 

 feeble spinulations. 



The origin of the plumose columns may be studied in sections like figure 5 and may be here briefly 

 sketched. A single long smooth style is formed with its rounded end buried in the basal homy plate, 

 the spicule projecting vertically upward. Spongin accumulates round the base of such a spicule, 

 forming a small mound. The spicule elongates and is, moreover, carried outwards by the elongation of 

 the spongin mound at its base. While this is going on the other spicules of the column develop around ' 

 and beneath the first-formed one. Small spinose styles are found here and there projecting, inde- 

 pendently, upwards from the basal horny plate of the sponge. These are doubtless incorporated in some 

 neighboring homy column that starts a vigorous growth, coming to lie on the side of such a column. 



In the incrusting sponges there are only a few microscleres, scattered through the trabeculae of the 

 interior and in the dermal membrane. They are small isochete, about 12-14/1 long, and toxas 16-24/1 long. 

 The pores are scattered irregularly over the dermal membrane. They open into large spaces (subder- 

 mal chambers) lying beneath the membrane. The oscula are small apertures, often 1-2 mm. in diame- 

 eter, found here and there over the surface. They lead into canals which extend in a horizontal direc- 

 tion, branching as they go, directly beneath the dermal membrane. Thus the large cavities found 

 beneath the dermal membrane (fig. 5) are of two kinds, some belonging to the afferent and some to the 

 efferent system. The sponge tissue of the interior or parenchyma is reduced to a set of anastomosing 

 trabeculae lying between the two canal systems. In the trabeculse are situated the small spheroidal 

 flagellated chambers. The trabeculae contain numerous granular amoeboid cells (amoebocytes), but 

 these are especially abundant in the layer of parenchyma which lies directly upon the basal horny plate. 

 This basal layer of parenchyma (fig. 5) lacks flagellated chambers. Imbedded in the trabecule or 

 basal parenchyma are abundant sperm masses and some small ova. Young sponges of this incrusting 

 type are frequently found to contain numerous larvae in various stages of development. 



Structure of a sponge with lobes. — The incrusting sponge as it grows older throws out lobular out- 

 growths that are more or less cylindrical. The sponges shown in figure 2 exhibit several such lobes. 

 Lobes of this sort have an extensive skeleton which consists of a reticulum of homy spiculo-fiber breaking 

 up near the dermal surface into independent terminal branches. The latter are arranged more or less 

 vertically to the surface and support the dermal membrane. Their structure is essentially like that of 

 the homy columns of the young sponge. It is obvious that such a skeleton arises through the continued 

 growth and anastomosis of the vertical horny columns of the young sponge. With the elongation of the 

 columns to form fibers, many styles come to be entirely included in the homy substance. 



The spiculo-fibers in the interior of the lobes consist of abundant spongin together with included 

 and projecting styles. The included styles are chiefly of the smooth type, but the small spinose stj-les 

 are also found occasionally included. Typical included styles measure 280/1 by lo/i, 260/1 by lo/i, i6o/x 

 by 8/1. The head is sometimes slightly enlarged, the spicule becoming a subtylostyle. The projecting 

 (echinating) styles are few and scattered, spinose or smooth, the two types intergrading. The spinose 

 type has numerous distinct though small spinulations on the shaft, and a minutely tuberculate, slightly 

 enlarged, head. Spicules with only a few scattered spines occur, and finally quite smooth spicules 

 with head end simply rounded and not enlarged. 



The terminal branches of the skeletal framework also possess included styles. Such branches break 

 tip each into a spreading tuft of long styles. Smaller lateral styles, projecting obliquely, some spinose, 

 some smooth, are also present. 



Quantities of young megascleres (very slender) are found throughout the sponge. The microscleres 

 are scantily present. They include isochelje 12-14/1 long, and toxas 30-40/1 long. The pores, oscula, 

 canals, and trabeculae of sponge parenchyma in such a lobe have essentially the same character as in the 

 incrusting type. Amoebocytes are abundantly present throughout the lobe. 



