250 r. ijiMA : hexactinellida. i. 



made no mention of this variability is probably due simply to 

 the fact that the ledges were not represented in the pieces 

 examined by him. After all I do not see in the organization 

 of R. decora any tangible point l)y which it may be upheld as 

 a valid species. 



Malformations in parts of the body, brought about after the 

 healing of injuries received by the sponge-wall, are as common 

 as, and present appearances similar to those in Euplectclla. 

 Let mention be made here of a remarkable case of regeneration 

 that came under my observation. 



Of a medium-sized specimen there remained only a small 

 lateral piece of the wall at its base, standing on the basal ex- 

 pansion ; the rest of the body had been torn off and lost. The 

 remnant shows the ledges and parietal oscula in a normal con- 

 dition on the dermal side. On the gastral side, which had be- 

 come directly exposed to the outer world, the loose sponge- 

 tissues had greatly increased, thus adding much to the thickness 

 of the wall. The thickening had become in one part all the 

 more considerable on account of the formation of a large cavity 

 right in the middle of the regenerated tissues. The cavitv evi- 

 dently served the part of a gastral cavity newly formed. On the 

 one side it is bounded by the old sponge-wall with its parietal 

 oscula ; on the other, by a thinner wall consisting of the re- 

 generated tissues, which are likewise perforated by a number of 

 roundish gaps, the parietal oscula of the new formation. Some 

 of these gaps are situated so close together as to form regular 

 sieve-plate beams between them. The above case seemed note- 

 worthy as illustrating the free formative jdasticity dominant in 

 the sponge-tissues. 



