A gizzard is present in a few forms. The buccal cavity is sometimes armed with jaws.
In some Indian and Malay Engystomatids of the genera Callula and Microhyla, the tadpoles are remarkably transparent, and differ markedly in the structure of the buccal apparatus.
This differentiation is not, however, peculiar to the Polychaetes; for in several Oligochaetes the anterior nephridia are of large size, and opening as they do into the buccal cavity clearly play a different function to those which follow.
Parapod.ia hardly projecting; palps of prosomium forming branched gills; no pharynx or eversible buccal region; no septa in thorax, septa in abdomen regularly disposed.
The buccal region is unarmed and not eversible.
Thus, in Octochaetus multiporus a large nephridium opens anteriorly into the buccal cavity, and numerous nephridia in the same worm evacuate their contents into the rectum.
A buccal cavity, a pharynx, an oesophagus and an intestine are always distinguishable.
There are two chitinous jaws in the buccal cavity, a dorsal and a ventral, which are of specially complicated structure in Cirrodrilus.
Bucc, Buccal mass.
- Nervous system of Patella; the visceral loop is lightly shaded; the buccal ganglia are omitted.
- Nervous system of Haliotis; the visceral loop is lightly shaded; the buccal ganglia are omitted.
B, Buccal ganglia.
V, Buccal cavity w, Gonad.
Two pairs of salivary ducts, each leading from a salivary gland, open into the buccal chamber.
The alimentary canal of the Pectinibranchia presents little diversity of character, except in so far as the buccal region is concerned.
(From Gegenbaur, after Jhering.) B, Buccal (suboesophageal) ganglion.
A crop-like dilatation of the gut and a recurved intestine, embedded in the compact yellowish-brown liver, the ducts of which open into it, form the rest of the digestive tract and occupy a large bulk of the visceral hump. The buccal region presents a pair of shelly jaws placed laterally upon the lips, and a wide range of variation in the form of the denticles of the lingual ribbon or radula.
- A, Triton variegation, to show the proboscis or buccal introvert (e) in a state of eversion.
A, Siphonal notch of the shell e, Everted buccal introvert (prooccupied by the siphonal boscis).
The alimentary canal commences with the usual buccal mass; the lips are cartilaginous, but not armed with horny jaws, though these are common in other Opisthobranchs; the lingual ribbon is multidenticulate, and a pair of salivary glands pour in their secretion.
Our figure of the nervous system of Aplysia does not give the small pair of buccal ganglia which are, as in all glossophorous Molluscs, present upon the nerves passing from the cerebral region to the odontophore.
T h e buccal nerves and ganglia are omitted.
C, Buccal ganglion.
No buccal appendages or suckers; a very long evaginable proboscis; a quadriradiate terminal branchia.
Of any kind; a short evaginable pharynx, bearing paired conical buccal appendages or " cephalocones."
No branchia; two long and branched buccal appendages.
The last three families constitute the sub-tribe Porostomata, characterized by the reduction of the buccal mass, which is modified into a suctorial apparatus.
59) is sufficiently described in the letterpress attached to it; the pair of buccal ganglia joined by the connectives to the cerebrals are, as in most of our figures, omitted.
The proboscis is not the only organ of locomotion, being assisted by the succeeding segment of the body, the buccal segment or collar.
Not only is the coelom thus subdivided, but the enteron (gut, alimentary canal, digestive tube) itself shows indications of three main subsections in continuity with one another: - (I) proboscis-gut (Eicheldarm, stomochord, vide infra); (2) collar-gut (buccal cavity, throat); (3) truncal gut extending from the collar to the vent.
The paired ctenidia are very greatly developed right and left of the elongated body, and form the most prominent organ of the group. Their function is chiefly not respiratory but nutritive, since it is by the currents produced by their ciliated surface that food-particles are brought to the feebly-developed mouth and buccal cavity.
The buccal glands are arranged in two ?., rows parallel with the molar teeth.
The two somites following the mandibular or first post-oral or buccal somite carry appendages modified as maxillae.
That the buccal gnathobasic parapodia (the mandibles) were in each of the three grades of prosthomerism only developed after the recession of the mouth and the addition of one, of two, or of three post-oral somites to the prae-oral region had taken place.
On the whole the facts seem to be against this supposition, though we need not suppose that the gnathobase was very large or the rami undeveloped in the buccal parapodia which were destined to lose their mandibular features and pass in front of the mouth.
That all the Arthropoda are to be traced to a common ancestor resembling a Chaetopod worm, but differing from it in having lost its chaetae and in having a prosthomere in front of the mouth (instead of prostomium only) and a pair of hemignaths (mandibles) on the parapodia of the buccal somite.
The second somite is the buccal somite (II, fig.
D, is the neuromere of the second III and IV, Coelom of the-third or buccal somite.
Of these facts is given by saying FP, Rudimentary frontal pro that the Onychophora are " deutercesses perhaps repre ognathous " - that is to say, that senting the prostomial the buccal somite carrying the mantentacles of Polychaeta.
The buccal somite, with its mandibles, is in Hexapoda, as in Crustacea, the fourth: they are tetartognathous.
The adhesion of a greater or less number of somites to the buccal somite posteriorly (opisthomeres) is a matter of importance, but of minor importance, in the theory and history of the Arthropod head.
In Diplopoda two opisthomeres - that is to say, one in addition to the buccal somiteare united by a fusion of their terga with the terga of the prosthomeres.