1908] Nervous System of the Larva of Corydalis 107 



INTRODUCTION. 



The Corydalis larva, popularly known under the name of 

 "dobson," "hellgrammite" or "crawler," is commonly found 

 under stones at the bottom of swiftly flowing streams. Three 

 years are required to complete the life cycle of the insect. The 

 pupal and adult stages are of short duration, so that almost three 

 years are required for the development of the larva. 



This, when full grown, measures from 80 to 90 millimeters in 

 length. It is rather oblong, depressed and tapering towards the 

 posterior extremity. The entire body is dark brown or nearly 

 black in color, with irregular markings on the chitinized portions 

 of the head and thorax. 



On either side of the head, caudad of the base of the antennae, 

 there are six simple eyes. In very rare instances are there devel- 

 oped seven perfect eyes, the rudiments of the seventh being indi- 

 cated by a light spot below the normal ones. 



There are nine distinct abdominal segments, the last of which 

 is provided with a pair of prolegs. The lateral borders of the 

 first eight abdominal segments are pushed out into so-called 

 lateral filaments. There is also a small pair of similar filaments 

 to be found on the prolegs. On the ventral side of each of the 

 first seven abdominal segments, there is a pair of large tracheal 

 gills of a brush-like appearance. These are w^ell supplied with 

 tracheae, which ramify rapidly and send off branches, one to 

 each separate thread-like portion of the gill. 



As might be expected from the systematic position of the 

 Corydalis, the nervous system of the larva is of a very generalized 

 type. There is a ganglion for practically each segment of the 

 body. Only in the last abdominal segments has there taken place 

 a cephalization by the fusion of two or possibly three ganglia. 

 The ^•arious ganglia of the central nervous system are connected 

 longitudinally by tw^o distinct nerve cords or connectives*, 

 thus forming a chain, which extends on the ventral side through- 

 out the length of the body. In the thorax and in the first abdomi- 

 nal segment, the ganglia are situated near the floor below the 

 large ventral muscles, while the succeeding abdominal ganglia 

 are all found above the same muscles. 



* In accordance with the suggestion of E. Yung '78, I have maintained 

 the term connectives for the longitudinal nerve cords, while the term commissure 

 has been used only for the transverse connections of sytnmetrical parts of the 

 ganglia. 



