Editing Onychophora (section)

===Digestion and excretion===
[[File:Peripatopsis capensis internal anatomy IMG 0781a.JPG|thumb|287x287px|Digestive system of ''[[Peripatopsis capensis]]'']]
The digestive tract begins slightly behind the head, the mouth lying on the underside a little way from the frontmost point of the body. Here, prey can be mechanically dismembered by the mandibles with their covering of fine toothlets. Two [[saliva]]ry glands discharge via a common conductor into the subsequent "throat", which makes up the first part of the front [[intestine]]. The saliva that they produce contains mucus and [[hydrolysis|hydrolytic]] [[enzyme]]s, which initiate [[digestion]] in and outside the mouth.

The throat itself is very muscular, serving to absorb the partially liquified food and to pump it, via the [[oesophagus]], which forms the rear part of the front intestine, into the central intestine. Unlike the front intestine, this is not lined with a cuticula but instead consists only of a single layer of epithelial tissue, which does not exhibit conspicuous indentation as is found in other animals.

On entering the central intestine, food particles are coated with a mucus-based [[peritrophic membrane]], which serves to protect the lining of the intestine from damage by sharp-edged particles. The intestinal epithelium secretes further digestive enzymes and absorbs the released nutrients, although the majority of digestion has already taken place externally or in the mouth. Indigestible remnants arrive in the rear intestine, or [[rectum]], which is once again lined with a cuticula and which opens at the [[anus]], located on the underside near to the rear end.{{citation needed|date=November 2014}}

In almost every segment is a pair of excretory organs called nephridia, which are derived from coelom tissue. Each consists of a small pouch that is connected, via a [[flagellum|flagellated]] conductor called a nephridioduct, to an opening at the base of the nearest leg known as a nephridiopore. The pouch is occupied by special cells called [[podocyte]]s, which facilitate [[ultrafiltration]] of the blood through the partition between haemocoelom and nephridium.

The composition of the [[urine|urinary]] solution is modified in the nephridioduct by selective recovery of nutrients and water and by isolation of poison and waste materials, before it is excreted to the outside world via the nephridiopore. The most important nitrogenous excretion product is the water-insoluble [[uric acid]]; this can be excreted in solid state, with very little water. This so-called [[uricotelic]] excretory mode represents an adjustment to life on land and the associated necessity of dealing economically with water.{{citation needed|date=November 2014}}

A pair of former nephridia in the head were converted secondarily into the salivary glands, while another pair in the final segment of male specimens now serve as glands that apparently play a role in reproduction.<ref>{{cite web |last=Holt |first=Jack |date=2010-02-07 |title=Introduction to the Onychophora |url=http://comenius.susqu.edu/biol/202/animals/protostomes/ecdysozoa/onychophora/onychophora.html |url-status=dead |archive-url=https://web.archive.org/web/20221005050117/http://comenius.susqu.edu/biol/202/animals/protostomes/ecdysozoa/onychophora/onychophora.html |archive-date=Oct 5, 2022 |access-date=2022-11-01 |series=Biol. 202: Systematic Biology |publisher=Susquehanna University |place=Selinsgrove, PA |quote=Excretory system: Pared metanephridia opening by their own ducts at each internal "segment". Anterior nephridia modified to salivary glands; posterior nephridia modified to gonopores. |department=Protostomes > Ecdysozoa > Onychophora}}</ref>