466 ASTKOSCLERA WILLEYANA, THE TYPE OF A NEW FAMILY OF SPONGES. 



the sections of the Lifu specimens which I have examined, though the presence of 

 such a system is indicated on the surfece of the remaining specimen (Fig. 1, a). It 

 may be that a well-marked system of efferent skeletal canals is not developed until the 

 organism attains a certain size, and it seems clear, from the Funafuti specimen, that 

 the systems are multiplied, perhaps by branching of those already existing, as the 

 size is further increased. 



In the basal region the canals are less numerous than at the upper surface, a 



Fig. B. Photogii.iph of part of an appboxi-mately median longitudinal section, bt reflected light. 



The skeleton (white) is seeu to be made up of separate elements. The skeletal canals (dark) are occupied 

 hy the (stained) soft tissue. 



result produced, as sections through this region show, by the closure of the canals by the 

 growth of the skeletal elements which border them (Fig. C, act). The elements increase 

 on the surface turned towards the canal till they come in contact with those of the 

 opposite side. Some canals in the base remain jjermanently open, and from these the 

 soft tissues are apparently withdrawn towards the growing surface. 



It may be well to mention here, what will be evident when the soft tissues are 

 considered, that though the large canals forming the systems above described are pro- 

 bably mainly efferent channels, the remaining skeletal canals, and by far the majority, 

 contain both afferent and efferent trunks of the water-carrying canals of the sponge. 



Mode of Growth. Fig. C represents a section through the specimen from which 

 Fig. 2 is drawn, whose axis has curved in the course of growth. The section shows 

 that the layer of growing tissue is not limited to the upper surface, but has, as 

 it were, overflowed for a short distance down that side towards which the growth 



