98 



A. OKA. 



0.02-0.04 mm. liiuh. The nucleus measures about 0.007 x 0.00 i mm. 



The basemeiit membraiïe situated directly Ijeneath the outer 

 celldayer is secreted either by this, or by the internal lining epithe- 

 lium, or by both. In the gretiter part of the cœnœcium where this 

 ]nembrane is separated from the inner epithelium l)y the muscular 

 laver, it would be natnral to refer its origin to the outer cell-layer 

 alone, but where the muscular layer is deficient, it is difhcult to 

 decide. On the other hand, in the wall of the funiculus into which 

 this membrane and the inner epithelium, but not the outer cell- 

 hiver, are continued, it cannot but be the jn'oduct of the inner 

 epithelium only. Generally, the l)asement membrane and the mus- 

 cular Go;it are treated as one layer under the name of Tunica nuis- 

 cularis, but as they are in reality quite distinct from each other, it 

 will ]je better to regard them as two distinct layers. AVlien a colony 

 is treated with a weak solution of acetic acid, the basement membrane 

 separates from the rest of layers. It is thin, tough., transparent, and 

 homoii'eneous. 



Next to the basement membrane conies the nuiscular layer, con- 

 sisting' of transverse and lomjitudinal fibres. The f3rmer run 

 external to the latter. They are not very densely set, so that in 

 a surface view they cross one another as in coarse linen. On the 

 main ]>art of the polypide, only the longitudinal fibres are present. 

 In such genus as Cristatella, the muscidar layer gives the colony the 

 power of slow locomotion, but what function it has to discharge in 

 fixed Pectinatella, I am not prepared to say. In the cœnœcium 

 where this layer is best developed, it is 0.005 mm. thick. It is not 

 found in that part of the endocyst wh.ere buds^ are formed, and is 

 also absent in the walls of the lophophore and the tentacles. 



The internal epithelial Inyer lines the endocyst everywdiere. It 

 is thickest in the cœnœcium, especially at those points where budding 



