78 



OLIGOCHAETA 



Fig. 22. 



HEART BODY OF ENCHY- 



TKAEID. 

 (After Michaelsen.) 



out that the flow of the blood forwards would be facilitated if the tube were 

 completely closed posteriorly during contraction ; the presence of this cardiac body 

 would help to fill up the tube, and allow the lumen to be entirely obliterated without 



reaching the maximum degree of contractility of the dorsal 

 blood-vessel. 



The genus Lumbriculus and other Lumbriculidae have 

 a series of caecal diverticula (woodcut, fig. 23) of the dorsal 

 vessel, which are clothed with large chjoragogen cells, and 

 are contractile ; these were formerly mistaken for caeca of 

 the gut itself, but there is no doubt that this was an error ; 

 they serve as temporary reservoirs of the blood, which is 

 presumably subjected during its sojourn in them to the 

 action of the peritoneal cells which envelop them. 

 Nothing of the kind exists in any worm that is not 

 a Lumbriculid, though they are not found in the Lumbriculid genus Stylodrilus. 



A third kind of blood glands (woodcut, fig. 24) are to be met with in various species 

 of the genus Penchaeta. They were originally described by PERKIER (3), who thought 

 them to be of the nature of salivary glands ; they occur in Perichaeta houlleti, for 

 example, at the sides of the oesophagus and show a distinctly metameric arrangement, 



being grouped in accordance with the segments. These 

 glands consist of a number of spherical acini, which have 

 a solid appearance, and are composed of small rounded 

 cells ; they have, however, as I (43) showed, no connexion 

 whatever with the gut, and are simply dilatations upon 

 the blood-vessels comparable to those dilatations which 

 occur along the course of the nephridial tubes, than which, 

 however, they are considerably larger ; a blood-vessel can 

 be traced into them and out of them. They are covered 

 externally by masses of pigment-holding peritoneal cells, 

 and form with these fairly compact glandular masses. 

 Something of the same kind appears to exist in at any 

 rate one species of Acanthodrilus, A. rosae. 



In the aquatic Oligochaet genus Phreodrilus another 

 variety of organ of possibly a similar physiological nature 

 occurs ; in the twelfth and thirteenth segments of this worm is a coiled tube which 

 puts the dorsal and the ventral vessel into communication ; it is so much coiled that 

 I have not been able to ascertain its exact shape ; the interior of this vessel, which 



LUMBRICULUS : BLOOD 

 GLANDS. 



(After Claparede.) 



i. Ventral blood-vessel. 2. Dorsal 

 blood-vessel. 3-5. Branches of last 

 with caecal twigs. 



