236 ANNELIDA. 



tine ; they are convoluted and tubular, arising from the ventral aspect of 

 the general cavity near the median line, curving upward around the 

 intestine, and terminating in a fan-shaped ciliated extremity, which is 

 bridled to the septum near its dorsalmost edge. Those segmental organs 

 which are situated anterior to the gizzard are very much larger and 

 more distinct than those that are placed behind it. 



(613.) The season of the year and the state of the weather have much 

 to do with the condition in which these organs are found. All the speci- 

 mens upon which the following examinations were instituted were taken 

 in the months of July and August, from a rich, loamy, highly cultivated 

 garden soil. This fact it is material to know, since nowhere in the 

 ordinary fields and meadows does this worm attain the same size and 

 plumpness. The generative nisus does not seem to reach its climax 

 until the worm has arrived at a certain period of age and fulness of 

 growth, so that, out of a hundred specimens, only ten or fifteen may be 

 found in that condition which is required for the successful prosecution 

 of these researches. 



(614.) In Lumbricus terrestris, each ring of the body is divided from 

 the adjacent ones by membranous partitions, which either completely 

 or partially isolate the fluid contents of each annular space. It is pro- 

 bable, however, that the fluid of the general cavity freely oscillates from 

 one extremity of the body to the other, through perforations in the 

 septa. But whether the spaces be isolated or not, the ' segmental 

 organs' which they contain have no connexion whatever with one 

 another. The following account is descriptive of all those which are 

 situated posteriorly to the proventriculus and the generative region. 



(615.) The tube which connects the free extremity with the fixed 

 end is extremely convoluted, and thickly intermixed with vessels. This 

 intermediate tube is divisible into three distinct portions. First, a 

 smooth-walled membranous part, which extends from the umbrella- 

 like termination to the camerated or cellular portion, which is vigorously 

 ciliated in its interior. The ciliary current sets from the free end, in 

 the direction of the fixed end. The next division of the tube extends 

 from the termination of the smooth membranous part to the commence- 

 ment of the third stage : this portion is not ciliated ; the walls bulge out 

 into lateral cells. The segmental organ in this portion is inextricably 

 blended and matted up with blood-vessels. The fourth division of the 

 tube stretches from the end of the celled portion to the commencement 

 of the muscular part : this again is strongly ciliated ; its walls are thick 

 and contractile. The last, outermost, or dilated portion, bounded ex- 

 ternally by the attached end, is almost invariably, in the months of July, 

 August and September, crowded with the ova and young of a Nematoid 

 Entozoon, which might easily be mistaken for the ova and young of 

 the Earthworm, an error into which Dr. Williams himself fell during 

 his earlier researches. This dilated muscular portion of the segmental 



