BIOLOGY AND STRUCTURE OF HYDROPHILUS CARABOIDES 653 



The hypodermal cells (PI. 27, fig. 9, hp) are distinguished from, 

 the ones just described by a smaller size. In the hollow of the 

 cartridges there is a trace of lighter protoplasm directly con- 

 nected with the protoplasm of the trichogenous cell. In this 

 place there are located cells which stain pale and have nuclei 

 containing but little chromatin, and which are evidently the 

 nuclei of the hypoderma of the cartridges. From beneath this 

 structure emerges a rather stout sinuated fibre, which ter- 

 minates in a darker widening with a slender terminal appendage 

 (PI. 27, fig. 9, n ? a, nervous fibre ?) ; the nervous fibre reaches 

 from the body-cavity to the trichogenous cell (PI. 27, 

 fig. 9, ns?). 



These setae can be characterized as dermatochaetae dupli- 

 thecatae, as their basal cup (the theca) is double. 



In conclusion, a few more words must be said regarding the 

 structure of the pleural appendages of H. caraboides. 

 The hypoderm and the chitinous cuticula are not distinguished 

 l)y any particular peculiarities from the usual integument of 

 the remaining parts of the body. They are covered with 

 chaetoids ; the terminal long hairs are connected at their 

 bases with nervous cells. 



The muscles are fastened to the lateral wall (Text-fig. 14, wt) 

 of the pleural appendage and their function is to contract the 

 appendage. Through the lumen of the latter pass slender 

 and few tracheae and the fat-body ; besides the indispensable 

 cells of the haemolymph are present. 



On the Nervous System. 



The central nerve-cord consists, excluding the cephalic 

 ganglia, of three pairs of thoracic and eight abdominal ganglia,, 

 of which the last ones, i. e. the tenth and eleventh, almost 

 touch each other, and the ninth is situated nearer to the 

 tenth than to the eighth. The thoracic ganglia are larger than 

 the abdominal ones ; the first abdominal ganglion closely 

 touches the last pair of thoracic ganglia. On the whole the 

 ganglia are disposed fairly equally, and the whole cord shows, 

 a more or less regular structure. 



NO. 264 Y y 



