LANTKI-ET-KISIIKS. 



121 -> 



ill tlif In iiiihiviiicliial ,i;niovt\ Kangehiians dcscrihed" 

 as sensory cells ;i nuiiil)er of cyliiidricMl eiiithelial cells 

 scattered in the skin and most iiiiinerous on the fore- 

 most part of the bod)-, furnished distally with a long, 

 stiff hair, iir(i\iiiiall\- with a ])rocess fo whirii the peri- 

 ])heral end of a nerve tihrilla attaches itself. In the 

 vertical dirnial fin around the anterior end of the liody 

 \'()(iT and YiNG remarked'' small, round or oval, trans- 

 parent ganglion cells, situated ofteiiest in the fork be- 

 tween two nerve twigs (tig. 870, e)- 



These organs of sense have indeed scarcely been 

 submitted as yet to adequate investigation; but so much 

 is kiiiiwn, that the rudimentary eye has the same struc- 

 ture as in the lower Polycha^tous worms, and the ol- 

 factory depression also finds its nearest jinatomical liomo- 

 logue in Nemertines, Turbellarians, and some other 

 worms. There is this difference, however, that in 

 Branch'wstoma both these organs are single, and that 

 the olfactory organ is asymmetrical, situated on the left 

 side of the body. The only further reason which might 

 be adduced for calling the anterior end oi Branchiostoma 

 ■A rudimentary head, is that the spinal cord, as men- 

 tioned above, dilates in front, though but slightly, into 

 a vesicle from which there originate two fairly sym- 

 metrical ])airs of nerves, the second pair larger and 

 more numerously ramitied than the other spinal nerves. 

 It is therefore not surjirising that some have proposed 

 to separate this animal into a distinct class, and ha\e 

 said: it is neither a vertebrate nor an invertebrate, it 

 is something between the two. 



The organs of generation (fig. 364, c) are a row 

 of saccate vesicles, free from each other and usually 

 numbering 'iti — 28 on each side in full-grown indivi- 

 duals, between the abdominal wall and the atrium. The 

 male and female can be distinguished only liy the con- 

 tents of the vesicles'; and the sexual products are iiro- 

 bably emitted, as a rule, through the atrial pore. Ko- 

 walewsky' and Hatschek', however, saw these pro- 

 ducts discharged through the mouth aperture; and one 

 of the females received by us from Bohuslan had several 

 ripe eggs in the mouth cavity, where they may easily 



arri\f, as 1 1 atsciikk has pointed out, id'ter first being 

 liberated, b\- tlu; bursting of the generative sacs, in the 

 atrium and then passing, through the clefts of the 

 branchial sac, into this cavity and out at its anterior 

 (sphincterial) aiicrture. 



As e\cretor\- organs in the full-grown JJraiicliid- 

 sfomu \\'eiss has adduced' a large amount of the epi- 

 thelial lining of the atrium, es])ecially on two tubiforin 

 prolongations of the said cavitj' which project into the 

 abdominal caNitx- pro|ier or cndom (atrio-crelomic fun- 

 nels). In this connection he also draws attention to ids 

 (iwu discovery of small, tubular glands (kidiieysV) si- 

 tuated at the top of the branchial tongue-bars (secon- 

 dary cartilaginous rods) and opening on the outer side 

 thei'eof into the atrium. 



The character of the genus and its relation to other 

 animals are best (!xplained, however, by the history of 

 evolution''. BrancliioKfoma dejiosits its ova (fig. 371, A), 

 ,,. // // /.' 



I) 



Fig. 371. A, an uiiiiiipreguated egg, witli tlie so-called polar body 

 (Riclitungskorper, R), a small body liberated from the egg and marking 

 that pole thereof at wliich the segmentation is most active. D, an 

 impregnated egg, witlv two oleavage-cells not yet quite divided from 

 each other. C, an egg segmented into 8 parts. D, an egg with 8 large 

 cells round the inferior pole and 5 sixteen-celled circles higher up. E, 

 optical section at the Blastula stage (simple sacculation), with the in- 

 ferior pole flattened, the commencement of its upward invagination 

 towards tlie inside of tlie wall of the upper pole. F, optical section 

 (■f an embryo in the Gastrula stage, with the above-mentioned in- 

 vagination completed. Each cell of the ectoderm {Ekt) is furnished 

 with a flagellum. Ent, entoderm, .answering to the lower part of the 

 Blastula wall in tlie preceding stage. Tlie Gastrula mouth (Cm) is 

 the downward opening. After Hatschek. X 140. 



" Arch. Mikrosk. Auat., Bd. XII (1875—76), p. .30.S. 



' Leitrb. prakt. vergl. Anat., Bd. 2, p. 361. 



' And also, according to VoGT and Yu.ng (1. c, pp. 375, 376) by the inner epithelial investment of the transverse ventral muscle, 

 this being developed into a kind of support for the organs of generation (deferent grooves?), different in males and females. 



'' Mem. Acad. Sc. Petersb., ser. yil, tome XI, No. 4, p. 1. 



' jStiul. iil). Entw. d. Amphioxus, Arb. Zool. Inst. Univ. Wien, torn. IV, H. 1. y. 14. 



/ Quart. Journ. Micr. Sc, n. ser., No. CXXIV (Nov. 1890), p. 489. 



•' KowALEWSKV, 1. c. and Arch. Mikr. Anat., Bd. XIII (1876 — 77). ].. 181: Hatschkk, 1. c, Ray Lankkster and Willey, Quart, 

 burn. Micr. Sc, n. ser., No. CXXIII (Aug. 1890), p. 445. 



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