314 



Bay correspond closely to those of L. Ugnorum and it should undoubtedly be included 

 in that species. 



The INTERNAL MORPHOLOGY of Limuoria is typical of the isopods. We have 

 indicated the general arrangement of the organs in figure 129. This drawing is a 

 reconstruction from a series of longitudinal celloidin sections, of a thickness of 50 

 microns. The plane of section of the figure is approximately median. 



The nervous system is modeled on the arthropod plan. The brain (br., figure 129) 

 occupies the anterior part of the head and is rather closely surrounded by the muscles 

 of the mouth parts. It consists of two main lobes, one on each side of the median 

 line. Dorsal to each main lobe is a smaller median lobe. Laterally and ventrally are 

 two large optic lobes which connect by a short nerve directly with the eye. The com- 

 missure which passes around the oesophagus is quite wide and connects with the wide 

 ventral nerve cord. There are four large main ganglia on the ventral nerve cord of 

 the head region (ga«g.'-<, fig. 129). Their peripheral connections cannot be stated 

 with certainty, although the first is probably the mandibular, while the last goes to 

 the maxillipeds and is, therefore, the first thoracic ganglion. The nerve cord passes 

 from the head to the thoracic region by a narrow connection. There are seven large 

 ganglia here (/-/, fig. 129), the first and third being the largest. The abdontinal 

 ganglia (I-V, fig. 129) are five in number and more or less fused with one another. 



The circulatory organs consist of the heart, pericardium, and connecting blood 

 sinuses. The heart {ht., fig. 129) lies in the median dorsal line within the pericardium 

 (pc). It extends from the anterior part of the fifth abdominal segment to the anterior 

 part of the fourth thoracic. In cross section it shows two small ventrally lying pear 

 shaped bodies of reticular tissue, which Hoek (1893) considers to function as valves. 

 In the longitudinal section figured, the entire median ventral extension of the heart 

 is not indicated, but it can be seen in the cross section (fig. 130, 2) to extend to the 

 digestive tract {int.). The arterial system, which is usually well developed in isopods, 

 has not been worked out. The pericardium is a large cavity partially surrounding 

 the ovaries and containing considerable reticular connective tissue. The irregular 

 spaces within the connective tissue are filled with blood on its way to the heart. The 

 lateral walls of the heart show thin strands running irregularly obliquely, which are 

 the contractile fibers of the heart. 



EXPLAN.^TION OF FIG. 129 



Internal anatomy of Limnoria lignoniin, reconstructed from sections. Median longitudinal view. 

 Magnification about 60 diameters. 



Antero-lateral process of gastric mill. 



Accessory organ of ovary. 



Anus. 



First antenna. 



Second antenna. 



Brain or supraoesophageal ganglion. 



Chitinous strands attached to the 



postero-lateral and postero-dorsal 



pieces of gastric mill. 

 Chitinous cuticula. 

 Connective tissue. 

 Ganglia of the ventral nerve cord in 



the head region. 

 Right ventral hepatic caecum. 

 Left dorsal hepatic caecum. 

 Heart. 

 Intestine. 

 Li .er duct. 



5, 6, 7. Ganglia of ventral nerve cord 

 I\', \'. Ganglia of ventral nerve cord 



lat. p. 

 m. an. 

 mand. 

 med. p. 



IIIO. 



muse. 



mxp. 

 niic. 



oes. 



nvar. 



p.-d. 



p.-l. i 



pe. 



pica. 



let. 



Lateral process of gastric mill. 



Muscles of anus. 



Mandible. 



Median process of gastric mill. 



Mouth. 



Muscles to floor of masticatory 



stomach. 

 Maxilliped. 

 Nucleus of ovarian egg. Yolk granules 



are shown around it. 

 Oesophagus. 

 Ovary. 



Postero-dorsal process of gastric'mill. 

 Postero-lateral process of gastric_mill. 

 Pericardium. 

 First pleopod. 

 Telson. 



in thoracic region, 

 in abdominal region. 



