20 



SPONGES 



a form resembling a cock's-comb. In the British species Leucandra 

 nivea, a spreading colony is formed, composed of numerous flattened 

 volcano-like individuals. 



In the cases where the persons of the colony are not distinct 

 from one another, the colony as a whole may have a form scarcely 

 differing from, or even identical with, that of the sponge individual, 

 and in extreme cases the colony can only be distinguished from the 

 individual by its larger size and greater number of oscula. Instances 

 of this are well seen in the genus Clathrina among Ascons, where 

 the full-grown colony forms a spreading mass of tubes. Typically 

 the individuals are indicated in these forms by cone-like elevations 

 of the tubar system, each surmounted by an osculum (Fig. 7, Cl. 

 clathrus). In some species of the genus, however, the sponge assumes 

 a very compact form, like a cushion when sessile (Fig. 6, Cl. 



osc.t 



Tentorium semixnberites, O.S. On 

 the left-hand, an older specimen with 

 numerous oscula ; on the right, a young 

 specimen with one osculum ; osc.t, 

 oscular tubes ; b, base of attachment. 



Fio. 32. 

 Ophlitaspongia seriata, Bwk. osc, oscula. 



reticulum), or more or less globular when stalked (Fig. 8, CL lacunosa), 

 and then the number of oscula alone indicates the number of 

 individuals. In other cases, again, the tubes may ramify in one 

 plane, forming an incrusting colony spread over stones or seaweeds, 

 from which oscular tubes arise at intervals. 



Instances of sponge colonies in which the form of the colony is more 

 or less identical with that of the individual are very common also 

 amongst siliceous and horny sponges. The best examples are seen in 

 massive forms, such as Eusponyia or Tentorium (Figs. 39 and 31), where the 

 separate individuals are quite indistinguishable from one another, and are 

 only indicated by the oscula. In such cases the composite individuality of 

 the sponge can scarcely be recognised ; it becomes simply a compact 

 growth in which the repetition of a number of similar and complete 

 physiological systems alone marks the primitive individuals. 



Most of the sponges in which the loss of individuality is most 



