Invertebrate Zoology. 



their contents. Does your specimen show the efferent 

 branchial vessels ? The branchio-cardiac canals ? 



In the injected gills note the course taken by the large 

 afferent and efferent vessels. Is the flabellum also supplied 

 with axial blood-vessels ? Examine the gill with a lens and 

 note the slender filaments. 



Make a drawing that will show the structure of the gill. 



The Nervous System. The specimens have had many 

 of the internal organs removed, but as the greater portion 

 of the nervous system lies ventrally, it has not been injured. 

 The system consists of a series of nervous centres, or ganglia, 

 connected together by longitudinal and transverse commis- 

 sures. Work out the following : 



The siipra-cesophageal ganglia will be found beneath the 

 rostrum at the base of the antennae. The right is intimately 

 connected with the left. Extending posteriorly and sur- 

 rounding the oesophagus, are the circum-Msophageal corn-mis* 

 sures, which are soon united by 



The infra-cesophageal ganglion which lies immediately 

 behind the oesophagus. 



From the infra-cesophageal ganglion the longitudinal com- 

 missures or connectives may be followed to the region of the 

 telson. 



How many thoracic ganglia are there? How many 

 abdominal ganglia? Are the ganglia of one series more 

 closely approximated than those of the other? Does the 

 number of ganglia in anyway correspond with the number 

 of associated body segments ? Do you find nerves running 

 from the ganglia to the surrounding tissues? 



Make two drawings of the nervous system, one as it is 

 seen from above, the other as it is seen from the side. 



