BY R. VON LENDENFELD, PH.D. 515 



approacli to them. I have been informed by Mr. Haswell, that 

 he has discovered a similar transition form in certain i-adiating 

 muscular cells round the stomach of a worm. 



That the membranes in question really are muscular is rendered 

 particularly evident by the great difterences in the degree of 

 depression of the skin which covers the lacunose askeletous parts of 

 the sponge, which are an indication of extensive movements. The 

 latter can only be caused by contractions of this membrane. 



This membrane is perforated at the base by the exhalent canals, 

 which lead from the skeletons portion of the sponge into the 

 askeletous part, taken up by the lacunse of the exhalent system. 



Nervous System. 



At its distal margin the muscular membrane described above is 

 thickened. (Plates 37, fig. 1, i.) 



In transverse sections through this distal thickening we find 

 that no spindle-shaped granular cells take part in its formation 

 but that it is composed of a highly colourable granular mass 

 in which large nuclei are contained. The latter are spherical and 

 measure 0-002 mm. in diameter. From the sides of this structure 

 granular threads extend in a tangental direction and from its 

 distal surface slender, straight, or curved spindle-shaped cells 

 arise. The distal part of these reaches the outer surface. The 

 cells are curved in such a manner that this part is always nearly 

 vertical to the surface. To attain a vertical position of the end it 

 becomes necessary for those spindle-shaped cells, which originate at 

 the side of the swelling, to curve. 



These cells measure 0'02 mm. in length. At the ends they are 

 0-0005 mm. thick, but in the thickest central part they measure 

 0-0U015 mm. across. They are filled with granular protoplasin, 

 which imbibes staining fluids very readily and is turned brown by 

 the action of osmic acid. In it we firid, in the central swelling, an 

 oval nucleus 0-002 mm. long and 0-0006 mm. broad, and a few 

 large and remarkable granules which appear particularly after, 

 osmic acid treatment as very distinct black spots. 



