NCDIBRAHCHIATA. 



NUDIBRANCHIATA. 



docU. Wasa tk* 



it neeives oaly OB* daoT; bat in UMM 

 rtod in Ik* liver. ON b* 



enter* through 



Individual 



parte. Thca. organs. 



vary bulky. aad oeo-py UM greater portion oT UM 

 Tfc ".In*! a ownmoo vestibule, 

 Bfe4ik. prooM. oa the right sid. of th. body, and 

 MM meatb. wV*B it U present 



of dnwbUoa and naptntton Bimilrt of contra! orgaas 



-arteri.s, veina, anu 

 ; aad of lamtoated, braBohed,orp*^Uoe.braocoi; 



iltoe.oraloBfth*..d*.ofth.back. 



TW ryUiah heart UM always immediately below UM akin of th 

 took, aad OMbt* of two ekambm. an aurkb and a ventricU, 

 i a paihartiuM. A brg. aorta pa.*. forwards, dUtri- 

 to th. rarioo. etiani; and th. blood U returned 

 to th. hart ID a partially aerated state, only a portion of it 

 aartec peeied tkroarh UVbraBehiax Th Mood system i. somewhat 

 sjusliiit fat each of i. UITM nuailM. of th. order. 

 Th. partial or 



*B of . 



, to wktok i* appended a veotricb or 

 . tack* 



blood into the rend and 



obtiao b probably provided with a com- 

 and BBS, in eoaneetion with it, a porUl 



io or portal heart, that lie. 



related U th. former ai an 



Tfce Boi of UM blood is rapid; th. pubstions of the heart varying, 

 to UM Mil opeeb*. from fifty to a hundred in th. minute. 



It is evident, from UM eta** of UM circulatory apparatus, that respi- 

 perf armed oaly la part by th. branch*. In all th. three 

 UM skin, which b covered with vibratib cilia, sets as an 

 t aoeaaory hnalhmg organ, and thus UM blood is returned to 

 Ik* heart to a partially aerated condition. 



TV* nartuus system UIMSU>* a high darn* of concentration, 

 to any other group of Molluscs,- -and is divided 

 UM cephalic or excito-motor ; 



tfeorktoofUMoaoel 

 seta, wfcba may b* del 

 .rsepra-aaduifra-OMG 

 asses; UM former ar* 



or sympathetic ; UMM two portion* inter- 

 ' la. Th* cephalic ganglia an situated at 

 and naturally divide themselves into two 

 nspsctively ojeophageal and buccal, 

 The Utter are attached to the buccal 

 'mar. lniBi.rtbt.ly nlated to th* ossophsgus, 

 lhy an always seated, and about which they, with their 

 i. form one or man eoaetricted collars. Th* two sets of 



Jly of thre* pairs of principal 



ganglia, nuasmiei tary may" bs fused or blended together, and of one 

 or tve arosesory pain. TBS principal ganilia an th. cerebroid, the 

 Waasatsl. sad Ike pedbl ; UM aconsory,- th. olfactory and the optic. 

 with regard to th. median line, there 

 side, Th* eenbroida are invariably 

 and an united by 

 being usually in 



'.'.: ' I ' \ : : : . - 



o latter of th. sam. 



Th* braachiali, aa well a* th. cerabroids, 

 ar* generally abeve Ik* alimentary tab*, and aw frequently fused with 

 them. M at to farm a atogb mam oa each aid* of th* median line. 



fib an oaitod to UM buccal by two long coin- 

 peas from UM under sid. of th. cerebroidi and 

 a Bid* oolbr th. buccal around that 

 commissure, passing between th. 

 complete! a second or gnat posterior 

 varies to length, in accordance 



They an ylind symmetrically 



Mag OB. of each pair oa either 



awn* Ik* OMopkagw ; they hold a central poaitioo, and a 



a wry *kart *n*jimieim aeram UM median line, being 



*** with Mk otkar. aad, when dtottoot, an oonnocto 



laiirii with tk. branchial aad padial . UMM two latter 



BJBBMS 



____ , , .. _,.. to UM channel of th. mouth, to 



UM HBS ea4 oral Hatoulis. also to UM veil, when it b formed by the 

 amm ef UMM bttarorpm*: tary bar. likewb. attacked to them UM 

 rUa-th. olfactory and UM optic, 

 rtrflmte nerrm to UM mantb or dorsal akin, 



sin : UM buoaal proper 



MM) talk* 







'? 1 b "J*??* 1 * "OBMroil. minute rariotuly 

 taMaar by opaa puxnaH f nrrvea, ipread 

 pnaatoal of UMM PMXOMI an-th. 

 tk. lo 



faaX tk. pylorie, 

 gnglk aad Ma 



i UM vtowral end 





- 



the tetMtiaal, UM bnncbul, 

 kav. abo bwn found in 

 aadekia. Th...j.tm 



s**k* an provided with *dltory capsubs, which 

 vfatBtsb MiliUa to all UM jeueia. exoent SmMt- 



only a aingl* Urge ipherical otolithe ; the auditory organ* thu, in 

 thM>, retaining their embryonic condition. Eye* are aloo unirereally 

 pnaent, and an only a little inferior in organisation to thoaa of the 

 nigber Oaatoropoda, The donal tentacle, are the organi of smell, 

 and, judging from their great development, thu MUM uiut be more 

 acute in moat of th. Nudibranchi than it in in any other mollusc, 

 with the exception perhaps of .Vattfiltu. Touch undoubtedly reside* 

 ererywhere in the skin, but in specialised in the oral tentacles and 

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

 probably the Mat of taste. 



The skin raries very much in thickness in the several groups. It 

 sppean to secrete the tenacious fluid that so abundantly exudes from 

 three animals; though that which lubricates the foot is probably 

 provided by a special gland. 



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

 founts, the little that we know of their habits U mostly gathered from 

 the observation of individuals kept in confinement, and consequently 

 under influences mon or less artificial 



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

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

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

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

 apparently enjoying the warm rays of the sun. Alderia modata has 

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

 and Itorit Inlamellata is frequently found exposed on rocks left dry 

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

 concealing themselves under stones and shelving rocks. Host of the 

 littoral tribes an found near to low-water mark ; though some few 

 kinds occur much higher up among the rocks, where they must r 

 several hours every tide deprived of water. Dorit pilota, AWu 

 papiUota, and Eolit nana, an generally met with in such situations ; 

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

 tide. 



The Nudibranchs partake largely of the sluggish cliar.icter of the 

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

 sion with these animals. This is 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 podia! 

 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 sides 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 Nudibranchs 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 is effected 

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

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

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

 brancha are never lighter than the water, even when fully expanded , 

 though in this state many of them are nearly buoyant. 



A species of Prplidia has been observed the Rev. K. T. Lowe to be 

 phosphorescent. 



t&Tue Nudi branchiate MoUutca are very sensitive to external influ- 

 ences, shrinking quickly from contact, and withdrawing their organs 

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

 coralline., they often detach themselves on being disturbed, and drop 

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

 erect their papilla, and sometimes agitato them in a convulsed msnner, 

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

 endowed with a motion independent of the others. On such occasions 

 urticating filaments an probably ejected from the tips of them organs. 

 The papilla! of Eolit, Dolo, Antiopa, and some other allied genera, 

 are very slightly 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 an quickly reproduced when the animal is in a healthy state; 

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

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

 supposed, vital organs. 



Tb.ir tenacity of life when kept in confinement varies much in the 

 different specie*, but is greater than in many other marine animals. 

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

 tb*m very senwbly, so that it is difficult to keep them alive in warm 

 weaUMT, particularly those from deep water. The littoral species can 

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

 oonelderahle time out of water in a moist saline atmosphere, but they 

 die almost immediately when deprived of moisture. Several species 

 hav. lived for month* in the aquavivarium at the garden* of the Zoolo- 

 gical Society, Regent's Park. 



