372 COMINGS AND GALLOWAY MORPHOLOGY OF TREPOSTOMATA 



Plate 13. — Morphology of the Trepostomata. 



Figures 32 to 39. — Sections of NicJioIsoncUa coruuJa n. sp.. skoicinri the minute 

 spines projcctino into the zocccia. 



The usual appearance of the spines is shown in figures 35 and 37. 

 In figure 33 are shown spines that are either excessively thin- 

 walled or solid. At n in this figure and in the adjacent spine arc 

 seen black bodies that may be bubbles. The appearance shown at 

 m is probably due to the double refraction of the calcite. Figure 

 38 shows unusually thick-walled spines and possibly excavations 

 (.T, .t') in the walls of the zocecium, opposite the lumens of the 

 siiines. The spines m and n appear to contain foreign particles. 

 The thin transparent lining of the zoopcium is continuous with the 

 walls of the spines. This feature is also shown in figure 'M. 

 Figure 39 shows the i-egion of the zoarinm in wliich the spines are 

 invariably found, together with the fact that they are usually on 

 the lower sides of the zooecia. Figiires 34 and 35 show the same 

 set of spines under different magnifications. This is also the case 

 with figures 36 and 37. Figures 32, 34, and 36, X 65. Figures 33, 

 35, 37, and 38, X 287. Figures 39, X 25. (150-5, 5; 175-6, G; 

 150-5, 5; 175-23; 175-6.) 



FiGUKE 40. — Longitudinal section of Heterotrypa pi'olifica. 



This figure shows four zooecia emerging at the surface of the 

 colony, with their walls completely intact and their proximal dia- 

 phragms all developed at the same level. The distance from the 

 diaphragm d to the distal edge of the wall represents the length 

 of a typical zocecium. In the zocecium z is shown the thickening 

 of the walls often seen in the neck region of the zocecium. In 

 species with cystiphragms. there is often a circlet of cystiphragms 

 at this level. X 65. (102-13.) 



Figure 41. — Tangential section of Mcrlia normani Kirkpatriclc. 



The sheaves of fibers or spicules that make up the wall of this 

 sponge, with the sharp lines of demarkation between adjoining 

 sheaves, are clearly shown, x 65. 



