30 



G. O. SAES. 



[No. 1. 



within the mandibular segment. It is provided with four pairs 

 of distinctly defined lateral valvular openings, each pair occurring 

 exactly in the midclle of the corresponding segment. Here, 

 the heart is connected to the body-wall by slender fibres, the 

 intervening parts being slightly instricted, whereby the dorsal 

 as well as the lateral edges of the heart acquire a regular 

 undulated appearance. The heart»has its greatest width across the 

 anterior part, located within the dorsal prolongation of the cervi- 

 cal division, whence it tapers somewhat posteriorly. Its posterior 

 extremity is abruptly truncate and furnished with a råtner wide 

 medial opening, whereas the anterior extremity contracts to a 

 short aorta, through which the blood introduced into the heart 

 is expelled. The lateral openings of the heart are each surrounded 

 by delicate concentric muscular fibres and limited by two 

 distinctly defined valvular lips. Likewise at the posterior extremity 

 of the heart a valvular arrangement would seem to occur, and 

 the origin of the aorta is marked off by two narrow lips closing 

 and opening at regular intervals. Of any other distinctly defined 

 blood-vessels no trace whatever can be found, the blood circulating 

 simply within lacunar interstices between the muscles and the 

 connective tissue. In the shell, as above stated, these lacunar 

 interstices have a very complicated arrangement, forming a richly 

 anastomosing net-work of blood-rooms. Along the dorsal line,, 

 however, the presence of a well-defined longitudinal blood-sinus 

 may be readily determined. 



d. The Genital System. 



The ovaries have the form of two elongate and rather wide 

 tubes, extending throughout the greater part of the trunk along 

 the sides of the intestine and a little below it. They are 

 instricted at regular intervals, forming in each segment rounded 

 expansions, those of the upper and lower side alternating to a 

 certain extent, whereby the ovary assumes a peculiar fiexuous 

 or twisted appearance. These organs are rather difficult to ex- 

 amine, save when filled up by the dark-green ovarian sub- 



