458 J. F. ILLINGWORTH 



ceral cavity. In the form of a thin sheet it covers all the organs in 

 the central part of the body, and extends down between the lobes of 

 the liver and on the sides of the stomach. This nephridium is 

 abundantly supplied with blood vessels which form a close mesh-work 

 throughout the whole tissue. The external slit-like opening (Fig. F 

 Exr) is in the mantle cavity, below and to the rigth of the anus. It 

 is situated on a papilla and is bounded by two thickened lips. The 

 reno-pericardial connection will be described when we come to the de- 

 scription of the genital organs. 



The left nephridium is so small that it might easily be over- 

 looked. In a fresh specimen, however, it is easily seen as a brownish 

 spot in the anterior wall of the pericardial cavity (Fig. 4 Ln). It is 

 situated below and to the left of the point where the rectum enters 

 the body wall, and may best be seen by removing the heart with the 

 section of the rectum which passes through it. This kidney has no 

 pericardial connection and no union with the right one, but by means 

 of sections I was able to see the duct which is given off from the 

 outer end and opens on the surface to the left of the anus. The ex- 

 ternal papilla is seen with difficulty in dissection, as it is placed back 

 in the angle of the groove at the base of the left ctenidium (Fig. G 

 Exl). This opening is, however, in its position almost symmetrical 

 with that of the right kidney. 



The reproductive organs. These are situated on the floor 

 of the visceral cavity and are exceedingly large, often equalling in 

 size all the other viscera taken together (Fig. 2 G). This great 

 genital mass is unsymmetrically divided into two great lobes lying 

 close together one on each side of the oesophagus. These are joined 

 posteriorly and extend to a conical point back under the mantle, en- 

 tirely filling that part of the visceral cavity. On the inner walls of 

 the cavity of the genital mass the eggs or sperm cells are produced. 

 These animals are dioecious. 



The genital cavity ( Gen. c) is well supplied with arterial blood, 

 which will be spoken of in connection with the vascular system. The 

 sexual products, eggs or sperm, simply drop ofif into the genital cavity 

 when ripe and pass out through the large conical oviduct (Fig. 2 G. d) 

 near the anterior end of the right lobe. This duct diminishes rapidly 

 in size as it approaches its termination just within the external open- 

 ing of the right nephridium (Fig. H). The end of the duct has two 

 lip-like appendages, which act as a valve, coming together if there is 



