ADHESION AND SPINNING 



from the mesogloeal line as fibers, almost to the surface. Straight and 

 thread-like in their proximal course, they arise and become ribbon-like 

 when halfway up. This ribbon-like part is wound in a spiral form 

 around the nucleus. 



Lying as a cap over the nucleus and the fibrillar portion is the glue- 

 forming cytoplasm with the vacuoles of adhesive substance covering its 

 outer surface. Just under these 

 vacuoles lies a layer of large, 

 round plastid-areas that represent 

 some secretory activity. They 

 have been suggested to be poison- 

 forming areas of the cytoplasm, 

 but they more probably represent 

 preparatory stages in the forma- 

 tion of the glue substance. A 

 very peculiar cap-like mass on the 

 distal end of the oval nucleus is 

 not as yet understood, and we can 

 assign no function to it. 



A few other cells are found in 

 connection with these. Some epi- 

 thelial cells are grouped about the 

 bases of the adhesive cells and 

 help support them. Outside of 

 them is a layer of covering cells 

 and during their growth a single 

 "cap cell" covers the six or seven 

 cells in the group and protects 

 them until "ripe." A few slime 

 cells are found near and among 

 them. 



Passing from the Ccelenterata to the Mollusca a somewhat new type 

 of apparatus for attachment is found in which the second steps in speciali- 

 zation have taken place, the invagination of the glue-forming cells and 

 the formation of this adhesive substance into strands used to attach the 

 animal to its living place. This apparatus is known as a byssus. 



Here it is the "foot" of the animal that develops the organ. This is 

 not because the "foot" of the mollusk is homologous to that of the ccelen- 

 terate but because both of them are used to rest on and for attachment. 



The common mussel, Mytilus, will provide a subject in which we 

 may see a well-developed byssus. This should be dissected out with a 

 scalpel, and also studied in a series of bulk-stained sections for a general 

 idea of the apparatus. When it is desired to understand the histological 



FIG- 373- Matured grasping cells of Beroe 

 ovata. sp.f., spiral fiber which extends from 

 the basement membrane (b.m.) and, ascend- 

 ing to the main cell body, winds in two turns 

 about the nucleus; x, centrosome-like body 

 on distal end of nucleus. Other letters indi- 

 cate same as in the preceding figure. (After 

 SCHNEIDER.) 



