TRANSACTIONS OF SECTION U. 629 



But further indications have been furnished to me by some experiments I have 

 made. 



If one impedes the excretion of the silk, at the end of larval life, the cell still 

 continues to produce silk, and this silk becomes accumulated within the protoplasm. 

 The cell-body becomes quite burdened with silk-spherules. But it was not easy to 

 put a stop to the excretion of the silk. I did not succeed in making a vivisection 

 and tying the gland itself, because it was not possible to preserve the wound against 

 the microbes, and the animal always soon died. 



I have sometimes succeeded in stopping the tube on the lip with collodion ; hut 

 the best way was always to tie strongly the whole body of the caterpillar at one of 

 the anterior segments. I have kept caterpillars tied in this manner alive for months. 

 Several larvae of Bombyx ruhi tied in four places and sectioned between two 

 ligaments have remained alive for three months, and several of these separated 

 Segments underwent the first stages of metamorphosis. The caudal segment was 

 always the last survivor. 



We may thus admit that the silk is made up within the protoplasm and cast 

 out through the meshes of the net-like membrane. A selection is made probably 

 by this membrane itself amongst the several substances that are mixed with the 

 liquid part of the protoplasm and the silk, or the substance that becomes the silk is 

 cast out. Possibly in the normal animal this substance acquires the qualities of the 

 silk only when it has reached the interior of the gland, but in the tied animal it 

 becomes real silk-substance in the cell itself. 



Now, with regard to the special apparatus of the common silk-duct. A 

 transverse section through it, as seen under a sufficient enlargement, shows that it 

 is a pressing engine. It consists of a chitinous cylinder with a strong and highly 

 elastic wall. The upper part of this wall presents a ridge projecting into the tube 

 and pressing upon the two connected silk threads. Powerful muscles are attached 

 in such a way that their action is opposed to the elasticity of the walls. So 

 their contraction causes the bore of the tube to be enlarged and the silk to be less 

 compressed by the ridge. 



The use of this apparatus seems to be : — 



1st. To regulate the diameter of the thread, which is often very irregular before 

 it has passed through it. 



2nd. Probably to regulate also the thickness of the thread. It is well known 

 indeed that the threads in the floss are thicker than those of the cocoon. 



As the result of all this, do we know now where the silk comes from ? Not 

 at all. In biology, researches onlj' serve to remove questions farther off; new 

 questions always arise. 



We must now ask how the cell makes the silk up. Does the nucleus play a 

 part in its production, as seems to be indicated by the changes of form and by the 

 fragmentation it undergoes during the making of the cocoon P The silk, like the 

 uuclein, the essential substance of the nucleus, has a strong affinity for colouring 

 matters. Would this physical property result from a chemical relation between 

 these two complex substances ? Is the silk derived from the nuclein ? Or, in the 

 other case, from which of the essential elements of the protoplasm does it take its 

 origin ? 



4. On the Placentation of ihe Viujong. 

 By Professor Sir William Turner, F.R.S. 



In this paper (which will be printed in externa in the * Transactions of the 

 Royal Society of Edinburgh, 1889') it was pointed out that the placenta of the 

 Dugong is zonary and non-deciduate. 



5. Observations on the Myology of the Gm'illa and Chimpanzee. 

 By Johnson Symington, M.D., F.B.S.E. 



This paper is based upon the dissection of a male gorilla and a female 

 chimpanzee. Numerous anatomists have published descriptions of their dissections 



