AU1)IT<')RY (lltCANS. 



120.5 



passes hc'liiiid iiit(j a third srmicircidar canal, caiialis 

 posterior (cp), tliat bends ui)\vards and afterwards for- 

 wards and inwards, ojjeiiiiip- into tlie uii])er end of tlie 

 superior sinus (s.s). 



Tlie superior division of the or^aii usually coni- 

 inuiiicates by means of a small ojieninir or a shoi-t tulx-, 

 canalis utriculo-saccularis {cus), in the l)ottom of the 

 utriculus, with the inferior division. The latter consists 

 of a saccate part, sacciiliis (s), which in most tishes 

 possesses beliiiid a ]iouch-like ajiiiendage, laf/eiin corh- 

 li'W (/), the first rudiment of the cochlea so riclily de\('- 

 loped in the liii;her animals and, above all, in man, 

 together with its highest develoijment (the organ of 

 Corti). From the inner superior side of the saccidus 

 there issues besides a narrow canal, ductus e)i(l<il//iiiji/i(i- 

 ticus, which as a rule lays itself on the membranes of 

 the brain and terminates ciecally, but sometimes, as in 

 the Elasmobranchs, ascends to the upjier surface of the 

 head, wiiere it has a free orifice. 



Of nerve-endirujs the superior division contjiins at 

 least 4, namely a large one in the bottom of the re- 

 cessus utriculi {macula ac. recessus utricuU, mu) and 

 one in eacdi of the three ampulht {cristce ac. ampulhe 

 anterioris, e.deriue, and pusterioris, cr), besides wjiich 

 there appears in most fishes at the bottom of the utri- 

 culus itself, in the neighbourhood of the opening into 

 the sacculus, a small nerve-ending [macula ac. neglecta, 

 mil). In tile inferior division may be found, within 

 the sacculus, a large ending {macula ac. sacculi, nis) 

 and in most cases another, posterior one {papilla ac. 

 lafjente, pi), which is situated on the wall of the pouch- 

 like cochlear appendage, as soon as this is developed. 

 Thus in some fishes the number of nerve-endings is 

 only 6, in others 7. These endings are everywhere of 

 the same structure, the epithelium which lines them 

 consisting (jf numerous cells (auditory or hair cells) 

 furnished with hair-like processes (auditory hairs) jjro- 

 jecting freely into the endolymphatic fluid, ;uid of 

 supporting cells set between the former and isolating 

 them. 



The acoustic nerve divides into several branches, 

 ^\■hich supply all these nerve-endings each with a bundle 

 of nerve-fibres. These fibres, each of which issues 

 trom a bipolar ganglion cell embedded in the acoustic 

 nerve and its branches, penetrate the epithelium of 

 the nerve- endings and ramify around the auditory cells, 

 <iver which they spin free terminal ramifications, with- 

 out being directly continuous therewith. 



Here we give s(jme figures (tig. ?)i\i) to illustrate 

 the various development of the auditory organ in carti- 

 laginous and osseous fishes, namelj' Vhimcera, Acipen- 

 scr, and Pcrca, adding a figure of Scijlliorhinus to show 

 further how the organ has developed a special ty|)e in 

 the Sharks and Kays. The auditory organ of the l^ung- 

 fislies and amphibians is most closely linked, among 

 the forms adduced here, to the Ganoid type, as shown 

 by fig. 3(52, E, which represents the a])|)earance of this 

 organ in Siren Uic.ertiiia. The iiresent, however, is no 

 suitable oi(])ortunity for a closer consideration of these 

 (inestions. 



From the above it appears tliat, as we have al- 

 ready pointed out, tin; auditory organ of jlfi/xine may 

 justly be regarded as the lowest known form of the 

 development of this organ among the vertebrates, but 

 that, the intermediate links being- absent, we can only 

 imperfectly sketch its |)hylogenesis. In Myxine a di- 

 vision into a superior and an inferior part has pre- 

 sumably not yet taken place, and the inner part of the 

 annular tube probably represents both utriculus and 

 sacculus, which is also indicated by the emission from 

 this part of the end(dym])hatic duct. The (juter part 

 of the annular tul)e jirobably answers to the anterior 

 (or the outer) and tlie posterior semicircular canals with 

 their respective ampullar. Possibly in the future, when 

 the development of Myxine has been brought to light, 

 some knowledge may be gained both of this t|uestion 

 and so many others, touching the systematic position 

 of this remarkable creature and its relation to the rest 

 of the vertebrates. 



In the anatomical structure of Mijxine we have 

 still to consider the orr/ans of ijeneration and in con- 

 nexion therewith the jiresent knowledge of the im- 

 pregnation and development. 



The structure of the orari/ and eggs has long been 

 known. In the abdominal cavity of most specimens is 

 found along the right side of the intestine a somewhat 

 lobate, longitudinal mesentery, within wliicii are en- 

 closed, as it were suspended, rather numerous ova of 

 varying dimensions. In small individuals these ova are 

 generalh' of insignificant size and rounded form, some 

 hardly visible U> the naked eye, other somewhat larger, 

 up to the size of a pin's head. In more full-grown 

 individuals many similar eggs are also found, but there 

 besides appear, as a rule, a number (10 — 1.5 or more) 

 (jf larger ova, which are always oblong, fusiform, mea- 

 suring in some cases only 3 — 10 mm., in others 11 — 12 



