() 



10 C. F. JENKIN. 



less radially, and " linked " into a meshwork pattern. They rommnnicate with tlie 



fastral eavitv cither in groups tlirough cxcurrent chambers {T. scotti) or 

 independentl}' (7'. aiitarcticm). 



Tenthrenodes scotti.* 



(riate XXML, Fig. 9; and Plates XXVIII. and XXIX., Figs. 16-27.) 



There are two specimens of this new species in the collection, the larger one perfect, 

 the smaller one a broken fragment. Both were fixed in osmic acid and preserved in 

 alcohol. The larger and perfect specimen is referred to in the following description. 



The spono-e as preserved is flattened so that the opposite walls are in contact. Its 

 shape in this flattened condition is shown in Fig. l(i. The length is 115 mm. and 

 the diameter (flattened) 32 mm. The colour is brown, owing to the osmic- acid, and 

 was probably white in life. 



The whole surface is covered with a iMinspicuous honeycoiiili pattern due to the 

 linking of the flagellated chambers. When slightly magnified the jiattern is seen t 

 consist of a principal network of larger and deeper meshes divided by a finer network 

 of shallower meshes (see Fig. 9). To the naked eye the meshes appear to be smooth. 

 The pattern extends up to the oscular edge, the size of the meshes diminishing 

 gradually from the middle of the sponge to the oscule. 



Ca.nal System. —The flagellated chambers communicate through contractile 

 apop\les with excurrent chambers, which open through irregular ports into the gastral 

 cavity. The canal system is extremely difficult to make out in this species, owing to 

 the very irregular shapes of the flagellated chambers near their bases and the erratic 

 way in which they are crowded together. The presence of the excurrent chambers can 

 be ascertained most easily by examining the gastral surface under a low power. The 

 ports in the gastral wall are large enough to allow the interiors of the excurrent 

 chambers to be inspected and two or three of the apopyles to be seen in each. 

 Sections cut either perpendicular or parallel to the axis of the sponge are almost 

 useless for demonstrating the structure, but serial tangential sections enable the 

 actual connections to be followed satisfactorily and bring out the peculiar " linked " 

 arrangement of the chambers admirably. Figs. 17-20 represent corresponding parts 

 of four tangential sections chosen for illustration from a complete series ; Fig. 17 shows 

 the ports in the gastral layer ; Fig. 1 8 the grouping of the chambers in the sub-gastral 

 layer; Fig. 19 the grouping higher up, where both large and small meshes occur; 

 Fig. 20 the grouping on the surface, where only large meshes occur, the smaller 

 ones not reaching so high ; the section includes the tops of most of the chambers, 

 but a few project further and therefore appear cut through. Several groups of cells 

 are numbered, and may be followed from one section to another. 



In order to show the structure more clearly, the group of flagellated chambers com- 



* This species, represented by the finest specimen in the collection, is named after the distinguished leader 

 of the Expedition, 



