CLONAL VARIATION IN PECTINATELLA 



ANNIE P. HENCHMAN AND DR. C. B. DAVENPORT 



The freshwater Bryozoan Pectinatella magnified pro- 

 duces, as is well known, lenticular statoblasts or winter 

 buds that carry at the margin hooks whose number va- 

 ries from 11 to 26. The statoblasts develop in the funi- 

 culus of the zooids. The zooids arise by budding from 

 embryonic tissue which is laid down even in the stato- 

 blast-embryo of the preceding generation. The zooids 

 of a colony are thus related as closely as possible, being 

 developed parts of one and the same germplasm. The 

 zooids of a colony are found in branches or twigs that 

 radiate from a center and, in Pectinatella, are thick, short 

 and blunt, forming a stellate colony. Many of these 

 corms lie in contact with each other on the surface of a 

 more or less spherical mass of jelly that is secreted by 

 the colony. The colonies are in close contact like the 

 facets of a compound eye. As the gelatinous mass in- 

 creases so does the area available for the colony and thus 

 additional space is allowed for their growth. 



Whence come the colonies that lie on the surface of any 

 one of the gelatinous masses ? In part they arise by fis- 

 sion of preexisting colonies. A given colony gains an el- 

 liptical shape and then constricts in the short axis; the 

 periphery of the colony is increased and room made for 

 new branches and new young buds. If all colonies on the 

 surface of a given mass arose thus we could refer the 

 origin of them all to the original colony that came from 

 the statoblast. But, unfortunately, things are not so 

 simple. For two statoblasts may germinate in close 

 proximity to each other on the same substratum and, 

 under such circumstances, the masses of jelly they se- 

 crete will flow together and form parts of a single mass. 

 Thus the gelatinous masses in nature are of two sorts: 

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