MECHANICS OF THE SPINNERET 



197 



sub ait 



STRUCTURE OF THE SPINNERET 



I am not aware that anyone has ever attempted to explain the mechanism of 

 Ihe spinneret of nemas. Manifestly the flow of the caudal secretion is controlled 

 at will. Watching this operation as performed by a free-living nema, one is 

 forcibly reminded of the facility with which spiders regulate the operation of 

 their spinnerets, and, as in spiders, so in nemas, there must be a definite con- 

 trollable mechanism for performing these operations. The structure of the 

 spinneret in Mononchulus venlralis may at least suggest the mechanical prin- 

 ciples exemplified. 



The Needle-Valve. As a rule the nema spinneret is so extremely minute that 

 its details cannot be deciphered. In Mononchulus ventralis the spinneret is 

 relatively large and its elements more or less resolvable, but since it is ventral 

 in this species instead of terminal, as is usual, its form may not be entirely typical. 

 In M. ventralis we find the duct of the spin- 

 neret to end externally in a conical depres- 

 sion near the end of the tail. This conical 

 depression leads to a short oblique tube 

 terminating internally at the valve of the 

 spinneret, vlv-vlv, Fig. 2. The valve belongs 

 to the class known as needle-valves, and the 

 needle, if such it be called, is an acute, fusi- 

 form affair, duplex in cross section, and 

 nearly half as long as the terminus of the 

 tail is wide. It is placed at an angle of 

 about 45 degrees with the axis of the tail, and 

 while its acute free distal end lies loose in a 

 cavity of obverse mold, its more or less 

 cephalated proximal end is connected with 

 the dorsal side of the tail by means of oblique 

 muscular fibres. The proximal part of the 

 valve is located in the midst of a vesicle (?) 

 to the dorsal side of which its proximal ex- 

 tremity seems to be attached; the embryo- 

 logical development has not been investi- 

 gated, but conceivably the needle is formed 

 by an invagination of the wall of the "vesi- 

 cle." Into the base of the more or less 

 ellipsoidal "vesicle" the ducts of the caudal 



... 

 glands empty. 1 he operation of the needle- part of the spindle-shaped 



valve is now easily understood. The internal 

 body pressure will of itself keep the needle- 

 Valve closed. Contraction of the muscular 



fibres already described serves to pull the 



needle loose from the mouth of the valve, 



and so permit an outflow of the secretion. The "needle" is composed of two 



elongated, ceratinous lateral elements joined side by side, and the orifice of the 



valve is composed of three elements, disposed in the form of a hollow cone 



about the distal half of the needle. 



Nervous Apparatus of Valve. Most of the foregoing features are shown in 

 Fig. 2. Necessarily the apparatus is supplied with the appropriate sensory and 

 motor nerves. The details of these latter have not yet been made out with 



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Fig. 2. Spinneret of Mononchulus ven- 

 tralis, with coagulated secretion attached. 

 The valve is partly open and the secretion 

 is pouring out. The three ampullae empty 

 into a common space round the proximal 

 jpindle-shaped valve-plug, 



pulled open by the muscle, msc vlv. All 



