GENERAL ANATOMY OF A CRAB. 205 



x. The reproductive organs of the male crab. 



The testis (Fig. 104, t) is very similar to the ovary, and 

 consists of two lateral portions and a cross-bar. Each 

 lateral portion gives rise to a very long, greatly convoluted, 

 transparent white tube, the vas deferens (Fig. 104, vd), 

 which passes into a straighter portion, the ejaculatory 

 duct (ed), opening on the coxopodite of the fifth pereiopod. 

 Carefully examine the base of this joint, and notice that 

 the duct is prolonged, outside it, as a soft white tube, 

 which runs into the base of the first pleopod, into which it 

 opens. 



y. The Nervous System. 



Another specimen should, if possible, be used for study- 

 ing the nervous system. It should be opened from above 

 by cutting away the carapace, and, if a fresh specimen is 

 used, it should be placed in seventy-five per cent alcohol 

 as soon as it is opened, and the dissection should be carried 

 on under the alcohol. 



Turn the cardiac pouch to one side, and notice on the 

 lower surface of the anterior portion two white small gas- 

 fric ganglia, each of which is joined to a large nerve, 

 which runs forwards to the floor of the anterior edge of 

 the carapace, near which it enters the outer end of one of 

 the cerebral ganglia. These are a pair of pear-shaped 

 ganglia, united to each other on the middle line of the 

 body, and giving off from their narrow ends nerves to the 

 eyes, the antennas, the antennules, the gastric ganglia, and 

 the lining of the carapace. 



They also give rise to a pair of msophageal commissures, 

 or small nerves which run backwards, one on each side of 

 the oesophagus, into the cavity of the sternal plastron. 

 Just behind the oesophagus these commissures are united 

 to each other by a transverse commissure ; and at the outer 



