igo8.] R- E. Lloyd : Bathynomus giganteus. gi 



On opening the abdominal carapace, a large empty space was seen on both 

 sides of the posterior half of the heart. These spaces were thought to represent the 

 pericardial cavity, the walls of which were so friable that they could not be defined 

 by dissection. Before any manipulation was performed it was noticed that these 

 cavities communicated directly with the heart by means of two patent apertures. 

 These apertures were oval in shape, and of the same size and appearance in every 

 respact. They appeared to be natural features of the heart's structure, for the fibres 

 composing the heart wall diverged to form them. These openings have the appear- 

 ance of being " ostia," but some little doubt was felt as to their nature, for they were 

 by no means symmetrical in their position on either side. The one on the right side 

 was situated on the highest part of the side wall of the heart, while the other was 

 situated much further forward and at a lower level on the left side wall of the organ. 



There is little doubt but that these openings are ostia, but the asymmetry of 

 their position is so unusual that until this can be confirmed in other specimens, one 

 cannot be quite certain as to their nature. 



The posterior end of the heart is somewhat dilated and comes to an abrupt 

 termination behind, where it touches the upper border of the telson. The large 

 arteries were traced only so far as they are shown in pi. x, fig. i. 



This description, incomplete though it is, will perhaps suffice to show that the 

 vascular system of Bathynomus is not unlike that of the other Isopods. The abdom- 

 inal position of the heart and the presence of eleven main arteries are well known 

 features in the anatomy of other Isopods. The fact that the eleven arteries in Bathy- 

 nomus are all given off from the anterior half of the heart, the posterior half being 

 free from them and being perforated by ostia, seems unusual among Isopods. In 

 Asellus, PoYcellio, Ligidium and other genera, the five pairs of arteries spring from 

 the heart at equal intervals along its whole length, while the ostia are situated in a 

 corresponding way. The heart of Anceas maxillaris has been figured by Dohrn (i8); 

 this organ shows four ostia which are not arranged in symmetrical pairs, but are distri- 

 buted irregularly on the surface of that organ. This is a parallel instance to the 

 supposed arrangement of the ostia in Bathynomus. 



The Nervous System. 

 After removal of the alimentary organs, most of the central nervous system is 

 displayed pi. xi, fig. 4). From this figure it will be seen that a portion of the 

 ventral nerve cord is hidian from view by the union of the sternal alar plates, the 

 posterior borders of which form a wide notch. A large ganglion lies in this notch ; 

 it is connected with the cerebral ganglia by two stout commissures which lie in close 

 contact beneath the alar plates, but diverge behind the pharynx to surround that 

 organ. The commissures were without visible ganglionic enlargements, hence the 

 large ganghon in the notch of the alar plates was at first considered to be the 

 sub-œsophageal ganglion [s.o.g., figs. 2, 4). Since, however, this ganglion did not 

 seem to suppl}'- the muscles of the cephalic appendages, which were supplied by small 

 filaments from the commissures anterior to the ganglion, some doubt was felt as 



