380 



COMMELYNACEJE 



COMMENSALISM 



share of the profits, without involving partnership 

 liability. The contract must be in writing, and the 

 lender ranks in a bankruptcy after other creditors. 



C/Ommelyna'cese, an order of petaloid mono- 

 cotyledons, all herbaceous, chiefly neotropical, of 

 which a few species are cultivated in herbaceous 

 borders on account of the beauty of their flowers, 

 notably spiderwort, or Tradescantia ( Virginica, and 

 other species), Commelyna ccelestis, &c. Others 

 are grown in hothouses, notably the peculiar 

 Cochliostemma. 



Commemoration, or ENC^NIA, the great 

 festival of the Oxford academic year, usually takes 

 place on the third Wednesday after Trinity Sunday. 

 It is of very ancient date, public exercises and 

 recitations having been held from time immemorial 

 in honour of the Act, or period when Masters 

 of Arts and Doctors complete their degrees. The 

 proceedings consist of a Latin oration in honour of 

 founders and benefactors ; the presentation of the 

 honorary degree of D.C.L. to strangers eminent in 

 science, politics, &c. ; and the recitation of the 

 Newdigate or English prize poem, the Latin prize 

 poem, and the Latin and English prize essays. The 

 more strictly academic and solemn portion of the 

 proceedings was frequently wont to receive scanty 

 attention from a great part of the audience ; and the 

 noisy humours of the gallery have often encroached 

 on the stately periods of the public orator. In 

 1876 the undergraduates were removed from the 

 special gallery they had hitherto occupied, and 

 distributed amongst the general audience, which 

 includes ladies and strangers as well as members 

 of the university. ' Commencement ' is the cor- 

 responding festival at Cambridge, where, however, 

 it is of less general observance. 



Coilllliendam, an ancient manner of holding 

 ecclesiastical benefices. When a living fell vacant 

 by the preferment of its holder, it was commended 

 by the crown to the care of a clerk, usually a 

 bishop in one of the poorer sees, to hold till a 

 proper pastor was provided for it. Such a living 

 was called an ecclesia commendata, and was said 

 to be held in commendam. A commendam in 

 ecclesiastical law may be defined as the power of 

 receiving and retaining a benefice contrary to 

 positive law, by supreme authority. Holdings in 

 commendam were abolished in 1836. COMMEN- 

 DATORS, in Scotland, in Roman Catholic times, 

 were stewards appointed to levy the fruits of a 

 benefice during a vacancy. They were mere trus- 

 tees ; but gradually the pope assumed the power 

 of appointing commendators for life, without any 

 obligation to account. This abuse led in 1466 to a 

 prohibition of all commendams except those granted 

 by bishops for six months and under. See ABBOT. 



Commensalisin ( literally, ' at the same table ' ), 

 the intimate, but never parasitic association of two 

 different kinds of organisms, for the benefit of one, 

 or very often of both. Of such advantageous 



Sartnerships there are so many different forms and 

 egrees, that no precise definition of the term 

 can be given. ( 1 ) Every one who has looked at 

 shore animals must have observed how often 

 mollusc shells, for instance, are covered with 

 sponges, hydroids, worm-tubes, acorn-shells, and 

 the like. But this is a purely external association, 

 and depends simply on the" fact that the shells 

 afford convenient anchorage for the free-swimming 

 embryos. In many cases no great advantage can 

 accrue on either side. The habit is comparable 

 to that of vegetable epiphytes upon trees. This 

 grade might be spoken of as mainly external and 

 unadvantageous association. (2) In other cases, 

 however, the association, though probably acci- 

 dental, brings its reward. When one sea-mat 

 ( Polyzoa ) grows entangled with another of greater 



vigour, or when different kinds of polyps are- 

 similarly associated, and that is often, there may be 

 distinct advantage to the weaker form, since with- 

 out becoming a parasite it enjoys the privileges- 

 of a messmate. Or the advantage may take 

 another form, when the associate is carried about, 

 by its bearer. Thus, Cirripedes are common upon 

 whales, and have evidently an advantage both 

 in security and continual freshness of feeding- 

 ground over those which adhere to fixed objects. 

 This grade might be distinguished as that of fixed 

 external associates with the advantage on one 

 side. ( 3 ) It is, however, evident that if a crab be 

 covered with acorn-shells, or polyps, or sponges, 

 there is no longer a one-sided, but 'a mutual advan- 

 tage. It is well for the sedentary growth to be 

 carried about continually to new pastures ; but 

 it is well also for the crab to be masked. Covered 

 with a rich growth, either vegetable or animal, 

 the crabs must appear all innocence, and like 

 walking- woods of Birnam, can steal unnoticed upon 

 their victims. A gasteropod may be similarly 

 masked by polyps, and doubtless gives and reaps- 

 similar advantages. This grade may be described 

 as that of fixed associates with mutual advantage, 

 to this extent, at least, that the weaker animals 

 are borne about, and the bearers are masked. ( 4 V 

 But a higher stage of fixed association is some- 

 times exhibited, that, namely, where the partner- 

 ship is deliberate, where the masked bearer is 

 not passively benefited, but is an active accomplice. 

 Probably the most striking case of such deliberate 

 partnership is that referred to (and illustrated) 

 under the article ANEMONE viz. the habit which 

 some hermit crabs have of bearing about sea- 

 anemones on the mollusc shell which they inhabit, 

 or even upon their claws. It would appear that in 

 some cases the crustacean deliberately chooses its 

 ally, induces it to fix itself on the shell or claw, 

 and takes care not to leave it behind at the epochs 

 of shell-changing. When deprived of its com- 

 mensal, the crab is 'said to be restlessly ill at ease 

 until another of the same species is forthcoming. 

 Off some parts of the British coast, the beautiful 

 sea-anemone (Adamsia palliata) is found envelop- 

 ing the mollusc home of a hermit crab ( Eupagurus- 

 prideauxii). The use of the sea-anemone as a- 

 mask, and also as equivalent to a stinging organ, 

 is obvious enough, while the hermit crab returns 

 the benefit by carrying about the sea-anemone 

 and giving it a share of the spoil. This grade may 

 therefore be described as deliberate partnership, 

 with mutual advantage. 



So far only fixed commensals have been spoken, 

 of, but organisms may be constantly associated 

 without being attached. Sometimes different 

 organisms, both plant and animal, are found in 

 almost constant association without any obvious 

 connection obtaining between them. In many 

 cases this companionship may be simply due to 

 the fact that similar environmental conditions suit 

 both. Small fishes are sometimes found as free 

 commensals within sea-anemones ; the Remora 

 (q.v. ) attaches itself temporarily to sharks and 

 other fishes; the little crabs (Pinnotheres, &c. ) 

 found living freely inside various bivalves are prob- 

 ably true messmates, and similar habitual partner- 

 ship is very common among crustaceans ; a brittle- 

 star is known to live as a free messmate on a 

 crinoid ; many worm-types are found in constant 

 though free associations with other animals ; and 

 the same habit is exhibited by some Crelenteratea 

 and Protozoa. Many of the insects which frequent 

 plants are in strict sense commensals, feeding not 

 on their hosts, but on other visitors, &c. In some 

 cases they form an actual bodyguard. 



Commensalisin must, of course, be distinguished 

 from Parasitism ( q.v. ), whether external or internal* 



