628 EEPOBT — 1889. 



MONBAr, SEPTEMBER 16. 



The following Papers were read : — 



1. Specific Characters as useful and indifferent. 

 By Professor G. J. Romanes, F.B.S. 



2. The Limit hetiveen the Continental and Abyssal Marine Fauna. 

 By the Rev. Canon Noeman, M.A., D.C.L. 



3. The Secretion of Silk by the Silkworm. By Professor Gustave Gilson. 



The silk is produced in a special apparatus communicating with a short tube, 

 which lies on the lower lip of the worm. The silk-producing glands consist of 

 two tuhes rolled up under the digestive organs. Both unite in the anterior part 

 of the body into one single tube, the common silk-duct. Not far from their point 

 of union these tubes receive the excretory canal of two accessory glands. 



The common silk-duct opens at the end of the spinning-tube on the lip. A 

 peculiar apparatus, whose structure and function 1 shall describe later, is to be 

 found in the middle part of this duct. The two glandular tubes are composed of 

 laro-e polygonal cells containing a ramified nucleus. The silk appears as a 

 transparent cylinder of a half-solid and viscous substance, filling the tube. The 

 worm stretches out this substance into a thread, which dries up when it reaches 

 the air, and becomes very hard. 



The two silk streams which leave the two glands do not mix into a single one. 

 They simply unite in the common duct, and become glued together by a sticky 

 matter, which is probably produced by the accessory glands. In this manner the 

 silk thread of which the cocoon is made up is a flat string composed of two united 

 threads. 



The silk is, without doubt, produced by the large cells that compose the walls 

 of the gland. But the question is, how do these latter work to fill the interior of 

 the tube with the silk substance ? and this is the point to which I have especially 

 applied myself. 



When one makes a section through the gland the silk appears as lying close to 

 the inner surface of the cells. But such sections do not explain at all the process 

 of the excretion of the silk. This half-solid substance, which is harder than the 

 substance of the cell, might be either a regular secretion-product or a result of the 

 total transformation of the protoplasm. It is now pointed out, indeed, that certain 

 soUd or glutinous substances constituting the membrane of many kinds of cells 

 take their origin by such a transformation proceeding layer by layer. In fact the 

 question was not so easy to explain as it might appear. However, I have now 

 arrived at the conviction that the silk is a regular secretion-product. 



I will give a short account of the observations that have induced me to form 

 this conclusion. In the first place the glandular tube is internally covered, on its 

 whole length, by a transparent membrane. This membrane is very thin and not 

 easily detected. It contains circular threads, and the spaces between them are 

 filled with a network-formation. It appears to be very hard and consistent. 

 During the metamorphosis of the caterpillar, when the cells are degenerating, it 

 remains visible later than the cells themselves. The silk, being then always divided 

 from the cells by a membrane, cannot be a result of the direct transformation of 

 the protoplasm. 



Secondly. The silk is, in fact, ordinarily not to be detected by any reagents in 

 the body of the cell, and that was just another support to the hypothesis of the 

 total transformation of the protoplasm into silk-substance. But in some cases the 

 silk becomes really visible within the body of the cell. At the end of larval life, 

 especially in other species than the common silk-worm, I have found in the cells 

 certain shining spherules whose reactions were just the same as those of the silk. 



