82 . Dr. S. Lov^n on a remarkable Sponge 



dermal layer. Its inferior end is thickened into a dilated base, 

 from which the fine root-fibres spread in branches, forming 

 loops, and having attached to them numerous grains of sand, 

 spicules of sponges, and Foraminifera. 



A closer examination has given the following results. The 

 dermal layer of the stem is thin, but tough, and may be drawn 

 ofi" in long pieces. It then shows a transparent uncoloured 

 protoplasma, full of small yellowish granular corpuscles, with 

 or without larger granules (fig. 4). In this parenchyma is 

 imbedded (fig. 5) a felt of very small siliceous spicules, spindle- 

 shaped, not inflated in the middle, furnished with a central 

 canal (fig. 6). When measured, these were found to be from 

 0*1 millim. in length and 0*0018 millim. in thickness to 

 0*08 millim. in length and 0*002 millim. in thickness ; the 

 mean length was 0*08 millim., and the relation between length 

 and thickness in one as 100 : 3*6, in another as 100 : 1*8, 

 the mean of eight measurements as 100 : 2*76. The granules 

 of the parenchyma are more discernible if prepared with gly- 

 cerine, while the spicules are more distinct in Canada balsam. 



Within the dermal layer the stem is made up of closely 

 packed spicules, held together by a relatively small quantity 

 of parenchyma (fig. 7). At first sight it seems as if the stem 

 were composed of very long, rather spiral filaments ; but a 

 closer examination shows the spicules to be very short, but 

 disposed in strings ; so that the whole has the aspect presented 

 in fig. 8. The spicules are all of the same type : they are 

 spindle-shaped needles (figs. 9, 10, 11), having near the middle 

 a slight but distinct globular inflation or nodule, and tapering 

 towards either end from that point, not in a straight line, but 

 forming together a very obtuse angle. It is owing to this 

 peculiarity that the needles, united in rows, produce the 

 slightly spiral structure of the stem. Every needle ends in a 

 fine but rounded point (fig. 12). They are more or less round. 

 The layers of which they consist are not to be discerned ; only 

 the exterior one appears in the transverse section (fig. 13) as a 

 very thin ring. They have a fine central canal, which, if the 

 needle is not broken, is closed at the point. When the infla- 

 tion in the middle is not larger than is shown in figs. 9,10,11, 

 the central canal goes through it without branching ; but if 

 the nodule has increased a little more in two opposite direc- 

 tions (as is shown in fig. 14), which is very seldom the case, 

 two fine but distinct transverse canals are seen to go ofi* cross- 

 wise from the central canal into its nodule or inflation. I 

 have not observed this formation of secondary canals in the 

 middle nodule carried further than shown in fig. 14 ; it is an 

 incipient branching, and appears also in other parts of the 



