422 ELIZABETH KINNEV. 



his own conclusions which he states as follows: 'The fibroin is 

 produced by virtue of the physiological function of the gland 

 cells, without reference to any part of the gland tube; the 

 sericin is, in its formation from fibroin, quite indifferent from 

 the physiological function of the cells; on the contrary this 

 transformation goes on merely physico-chemically." 



Maziarski ('u) in his enthusiasm for the nuclear origin of 

 secretory products, states that the nucleoli which leave the 

 nucleus become the fibroin and that chromatin, likewise, may 

 be extruded into the protoplasm, there to undergo quite extended 

 changes and finally pass out into the lumen as the sericin or 

 gummy covering of the silk thread. This idea was not entirely 

 new, for Vorhies ('08) had suggested that chromatin material 

 may have a secretory function in addition to serving as the 

 "bearer of heredity." 



Nakahara ('n) recognizes only the formation of silk from 

 transformed nucleoli, but Yamanouchi ('22) describes the pro- 

 duction of sericin and fibroin in great detail and concludes that 

 fibroin secretion takes place only in the posterior region, but 

 that sericin secretion occurs in the posterior and middle parts 

 of the middle region. The two kinds of secretion appear alter- 

 nately and, due to the fact that each kind tends to remain 

 separate, two layers are formed, distinguishable by their different 

 staining reactions. 



Blanc ('89) has described a third product of secretion, called 

 by him " mucoidine," which envelops the silk fiber and stains 

 more intensely with methyl green than either the fibroin or 

 sericin. This substance, he thought, is formed in the anterior 

 portion of the reservoir and may serve the function of a lubricant, 

 thus facilitating the passage of the silk. 



(b) Observations.- From a comparative study of silk gland cells 

 prepared in different fixatives, it is evident that there exist in 

 the lumen, substances which show different types of reactions to 

 stains. After Regaud fixation, the silk thread appears to be 

 perfectly homogeneous throughout its entire extent except in the 

 .interior region of the gland where a slight ly darker band may be 

 distinguished around the thread. (Fig. 9.) The secretion found 

 in the posterior and middle portions takes a reddish-blue stain 



