On the Structure of an Earthworm allied to Nemertodrilus, Mich., with Observations on the Post-embryonic Development of Certain Organs
Authors: Beddard Frank E. 
Published: April 2021

The principal new facts in this paper may be briefly summarised as follows:

(1) The nephridial system consists of paired nephridia which do not open immediately on to the exterior, but are connected with an extensively ramifying system of tubes embedded in the circular and longitudinal muscular coats; these tubes consist of four principal longitudinal trunks continuous from segment to segment, and of a single large circular vessel in each segment passing right round the worm at the junction of the circular and longitudinal muscles; these are connected by a plexus of vessels, and numerous tubules, leading to the exterior, are given off from the circular trunk. In some of the genital segments the paired nephridia have almost disappeared, leaving only the integumental network. Nothing of the kind has been yet described in any Oligochæte. In the young worm, just escaped from the cocoon, there is nointegumental network, which must, therefore, be regarded as secondary, but the anterior nephridia at any rate are connected on each side by a continuous longitudinal duct lying within the coelom.

(2) In the young worm the reproductive organs agree with these organs in other earthworms; in the adult, a large unpaired sac lying over the gut is developed; this sac encloses the receptacula ovorum, and opens by a median pore on Segment 13. It is developed from mesoblastic tissues, and is not therefore the morphological equivalent of the spermathecæ in Lumbricus, &c., but it performs the same function; the sac is formed internally and then grows out towards the epidermis; it is at first in open communication with the cœlom; its front wall is formed out of the intersegmental septum between Segments 12, 13; the ovaries are enclosed by it, but disappear early, before the sac is completed; otherwise the ova would be probably unable to enter the egg-sac which becomes nearly completely shut off from the sac; the two are in communication only by the oviducal funnel, which has become divided by the growth of the spermathecal sac into two separate tubes, one opening into the spermathecal sac, the other into the closed egg-sac; they unite, of course, to form the oviduct itself, which opens on to the 15th segment, reckoning by the external furrow, but on to the border line between Segments 14, 15, reckoning by the septa.

(3) The testes and the vas deferens funnels are quite typical in their structure and position; so, too, are the (two) pairs of sperm-sacs (in Segments 11, 12). The sperm ducts are not, as they are in other Eudrilidæ, dilated to form sperm reservoirs; they open into tubular atria, with thick muscular walls and glandular lining, near to their blind extremities; the two atria open by a common pore upon the border line between Segments 17, 18; each is furnished with a short penial seta not ornamented.

(4) The alimentary tract has no calciferous glands or ventral œsophageal pouches such as are found in other Eudrilidæ; at the end of the œsophagus are three gizzards, one to a segment; the intestine which immediately follows has at first three typhlosolar folds; later on the two lateral and shorter folds disappear. The ventral wall of the pharynx is connected with the nephridial tubes of its segments; they open into the interior of the pharynx.

(5) The area surrounding the setæ of each side of the body is shut off from the general body-cavity, forming a paired series of chambers; in the œsophageal region is developed a perihæmal cœlomic space surrounding the subœsophageal vessels.