NfDIBRAKCHIATA. 



NUDIBRANCHIATA. 



UM gastric of 

 H rVoaiv*. only OM duct; bat In 



IB UM Uv*r, UM bit* raters through 



ar* hermaphrodite., each individual being 

 lit anil, f mull, ml mil U i r"~" The*, organ*. 

 UMT. are *ry batty, aad occupy UM greater portion of th* 

 They oocaaraaieate with a common T*.libule, 

 MSB an UM right aid* of UM body, and 



sad reaptrarion eooaUt of central organ* 

 aad portal b*ert,-arteri*a, reiaa, and 

 .; aad of laminated, branched, or papiUoasbranohi>; 

 r UMBMdi* Una, or along th. aid- of the back. 



rt IMS alway. immediaUly below the akin of the 

 back, aad ooaaMte of two chambers. an auricle and a ventricle, 

 I wMhia a peikmrdfaua. A large aorta pas*** forwards, distri- 

 wanes to UM Tarioo* organs; and UM blood i* returned 

 UM heart ia a partially aerated slate, only a portion of it 

 dthroh UVbraochiax Th* blood lyatom is aomewhat 

 . _i amoh ofUM tar** famflie* of UM order. 

 Th. partial or irBltii circulation is probably provided with a com- 

 fete *r*tom of eapOlarMS, and baa, in connection with it, a portal 

 ahaamlllB. to which ai apoanded a ventricle or portal heart, that lie* 

 , UM latter being related te th* former a* an 



nM 



hi UM 



portal heart propel* venom blood into the mud and 



UM blood i* rapid ; the pulsations of the heart varying, 

 fifty to a hundred in the minute. 



It to widest, from UM state of tb* circulatory apparatus, that respi- 

 i* parf armed oaly ia part by UM branchi*. In all the three 

 K, UM akin, which i* covered with vibratile cilia, acts a* an 

 C organ, and thus the blood i* returned to 

 doonditi 



UM (Mart la a partially 



.,,.. .. ;.,.:.. 



system present* a high degree of concentration, 

 ia any other group of Molluscs, and is divided 

 UM cephalic or excito-motor ; 



tie or sympathetic ; then two portion* inter 

 poiat*. Th* cephalic ganglia ar* situated at 

 Mrua, aad naturally divide themselves into two 

 may be ilanialn*t*il respectively OMOphageal and buccal, 

 or sopra- aad mtrm^Baaphaf**! Tb* latter are attached to the buccal 

 ma**; UM fnrmar ar* more immediately related to th* raaophaRtu, 

 which they ar* always wated, and about which they, with their 



" collars. The two seta of 



,- ntully of thre* pain of principal 



may be fuaed or blended together, and of one 

 j i-r.. The principal ganzlia ar* th* oerebroid, the 

 aad UM pedial ; UM acormory.-th* olfactory and the optic. 

 '**"' " ' ' '' n - with regard to the median line, there 

 Th* oerebroids ar* invariably 



ar tw *e****ary pain. The principal 

 htaaahUL aad UM pedial * *V^ acotaaM 

 They r* alacad *ymmtrically with r. 

 hsaag *a*of amh pair ea cHhar aid*. 

 aVm UM atwphafiii ; UMy bold a on 



m\ VHy ffl^* 9tNDBBW*aMt*TV aMPOtM 1*9*9 



aaBBBmtakaam ilij. ^auaV -**- - J mwk^mt A\ 



CwBaWmaC* 1UI VBOal O*J*WC, aUkO, W1NQ Q\ 



In mi wish UM braachial and padi* 



mmW atammt ^^^M^^^^BmammmmamaaamV TWal llVWa 



isnnl eara*. wM 

 emanatUMtmllet. 

 aha, A lent, m 



BS*^*Bk * BBW W >U1 



UMy bold a oratral poaUioo, and are united by 

 POT* aero** th* median line, being usually in 

 "MB distinct, ar* connected by com- 



pedial : the** two Utter of th* same 



The branchial*, as well as the cerebroida, 

 j tab*, and are frequently fuaed with 



^ on each aid* of tb* median line, 



U an united to UM buccal by two long com- 

 pam from UM under rid. of th. oarabroTd* and 

 a wide collar the buooal around that 

 ooaumanm, paasing between the 

 a necond or great posterior 



varies in length, in accordance 



- T U ^"y * " bor * alimentary 



to wag ; if partly babw, very abort. 



anhrvU gaafli* fir. aem* to UM channel of UM mouth, to 

 and are! Hulauln. aUo to th* veil, when it I* formed by th* 



, . .._ 1. .__ l.L_ __:__ a t i a_ . i . .1 



UM , r-W- <* UM 

 taha.ki*laag; 

 



rm vmfm^mr^u wi MV UIUUVU. W 



! **td oral tiBUiUa. al*o to UM wil. when it I* formed by UM 

 N*toBj< UM*. i lattar of^ : UMT oa* likwi* atUcbed to them UM 



^ ' '. ' . ..":? ."J..**" ..P" e '. 



"tftL 



aadtoth* 



to tbemantU or donal akin, 



_ -- to t*M fool, 



areeaoarally two pairs: th. buccal proper 



minute varionily 



by open pUxtum uf nervea, ipread 

 of UM* pUxnsa* ar* UM 

 i mteiUnal, UM branchial, 

 have also besn found in 

 .ndakiB. Tb...yrt4.m 



Uuw*> UM Tteaml aa>4 



'*.* aM a iwfew *f Ate (/WrettM 



with aodhory capmha, which 

 all UM inner*, exotpt BmU* 

 i and T^fiftt), whm Uwr* i* 



only a aingle Urge ipherical otolithe ; the auditory organ* thus, in 

 the**, retaining their embryonic condition. Eye* are aUo univeraally 

 praeent, and are only a little inferior in organisation to thoae of the 

 higher Oaiteropoda. The donal tentacles are the organ* of *m*ll, 

 and, judging from their great development, thi* sense innit be more 

 acute in moat of the Kudibranchi than it is in any other mollusc, 

 with the exception perhaps of \a*lilu*. Touch undoubtedly reside* 

 everywhere in the akin, but U specialised in the oral tentacle* and 

 part* about the mouth. The lip* and channel of the mouth ar* 

 probably th* seat of taste. 



The akin varie* very much in thicknes* in the several groups. It 

 appear* to secrete the tenacious fluid that so abundantly exude* from 

 three animals ; though that which lubricate* the foot is probably 

 provided by a special gland. 



As it is seldom possible to study these animals in their native 

 haunts, the little that we know of their habits is mostly gathered from 

 the observation of individuals kept in confinement, and consequently 

 under influence* more or less artificial 



Some of the species are nocturnal, but this is not the case with many 

 of the littoral tribe*. Such of these as are gregarious on small sea- 

 weeds, as Polycera quadrilintata, may be observed in a state of 

 activity during the day time, in tide-pools left among the rocks, and 

 apparently enjoying the warm rays of the sun. A Ideria modata ha* 

 a similar habit in more shallow water, becoming almost amphibious : 

 and Dorit biiamtHata is frequently found exposed on rocks left dry 

 by the tide. But the greater number of the species avoid the light, 

 concealing themselves under stones and shelving rocks. Ho*t of the 

 littoral tribe* are found near to low-water mark ; though some few 

 kind* occur much higher up among the rocks, where they must remtun 

 several houn every tide deprived of water. Dorii pilota, A'utit 

 papilloia, and Eolii nana, are generally met with in such situations ; 

 even the spawn of these species U frequently left dry by the receding 

 tide. 



The Nudibrancbs partake largely of the sluggish char.icter of the 

 class to which they belong. Crawling is the usual mode of progres- 

 sion with these animals. This U effected in the manner of the snail, 

 by a series of minute undulations of the under surface of the foot, 

 arising from the, alternate relaxation and contraction of the pedial 

 muscles. None of our native species have the power of swimming 

 freely through the water ; and we are not aware of any means they 

 have of reaching the surface but by crawling up any substance in 

 contact with it This they do frequently in confinement, by ascending 

 the side* of the Teasel, and then launching themselves, with outspread 

 foot, on the surface of the water in an inverted position. Like most 

 of the other aquatic Gasteropoda, they are very fond of floating in 

 this way, which they do without any apparent effort. 



While floating in this manner the Nudibrancbs occasionally drop 

 suddenly down, suspending themselves from the surface by a thread 

 of mucus, which is fixed to the tail or posterior extremity of the foot 

 In this way they will let themselves gradually down to the bottom, 

 or remain some time pendent in the water without apparent support; 

 for the thread of mucus is so transparent that it can scarcely be seen. 

 On any of these occasions, either when floating or when suspended, 

 if alarmed, the animal falls at once to the bottom. This i* effected 

 by the foot quitting its hold of the mucus, when the animal, being 

 upecifically heavier than the water, of course sinks; its specific gravity 

 is, no doubt, increased by the collapse of the parts ; but the Nudi- 

 branch* are never lighter than the water, even when fully expanded , 

 though in this state many of them are nearly buoyant. 



A specie* of Ptplidia has been observed the Rev. K. T. Lowe to be 

 phosphorescent. 



Tbe Xudibranchiate Mollutca are very sensitive to external influ- 

 ence*, shrinking quickly from contact, and withdrawing their organs 

 on th* least sense of danger. When crawling on sea-weeds or 

 conllines, they often detach themselves on being disturbed, and drop 

 to the bottom of the water. The Eolidti, when alarmed, or irritated, 

 erect their papilla!, and sometimes agitate them in a convulsed manner, 

 directing their apices to any source of annoyance ; each papilla being 

 endowed with a motion independent of the others. On such occasion* 

 urticating filament* are probably ejected from the tip* of these organs. 

 The papilla; of Kolit, Doto, Xn/ioy,a, and some other allied genera, 

 are very (lightly attached to the back, and the animals appear to have 

 the power of casting them off voluntarily, in the same manner as a 

 crab throws off its claws, or a star-fish its arms. The organs thus 

 cast off ar* quickly reproduced when the animal i* in a healthy state; 

 and what seems strange is, that in the meantime it does not appear to 

 suffer any inconvenience from the lost of these, as might have been 

 supposed, vital organs. 



Their tenacity of life when kept in confinement varies much in the 

 dmVant species, but is greater than in many other marine animal*. 

 Any impurity in the water, or too great change of temperature, affects 

 them very sensibly, *o that it in difficult to keep them alive in warm 

 w*athr, particularly those from deep water. The littoral species can 

 twtain a greater change of temperature, and may be kept alive for a 

 considerable time out of water in a moi*t saline atmosphere, but they 

 die almost immediately when deprived of moisture. Several xpecies 

 have lived for months in the quavivarium at the garden* of the Zoolo- 

 gical Society, Regenf* Park. 



