Tin: -1.1:11 LARID^E. 31 



The most complicated gonosome found in the Sertularidse is that illustrated h\- It 

 rxi i <<.<! and several other species of the same ovnus which appear to possess an aerncvst which 

 is itself inclosed in a liiarsii]iial cliamlier ilio>. '-M. Hi'). This very remarkable strueture was titst 

 described with cafe by Profe.ss< >r Allllian.' and this description still remains the best that I ha\e 



seen, although it contains some inaccuracies that will shortly lie pointed out. I have made a 

 careful study of f)iji/nix!,i f,i/l,i.r. both entire and in serial seeticins. with the following result-: 



A very youiij; female <? ..... ino-ium (see lio;. '.):',) is a club-shaped chitinous ])ellicle within which 

 the young blastostyle grows as a direct derivative of the c(enosarc of the stem. At its verv 

 summit is a larov ovum enveloped apparently in loliular diverticula from the lila-lo.-t vie, 

 another and smaller ovum beiiio- seen a short distance below. At a later slao-e the ^onanoMum is 

 obconical or trumpet-shaped (see lio-s. UK '.<:<). and the blastostyle has expanded so as to till it-- distal 

 portion with a sort of phi" 1 . At this staoy the summit of the e-onan^ium is convex, or bowl- 

 shaped, with the aperture in the center of the bowl, just above the axis of the blastostyle. The 

 rim of this bowl now LITOWS rapidlv, forming four broad scallops, and ultimately four broad 

 leaves, which are really flattened tubes of chitin. From the peripheral portion of the distal end 

 of the cirnosarcal plug (deckenplatte) four lobes composed of ectoderm and endoderm project 

 into the flattened tubes of chitin just mentioned and doubtless furni-h material for the growth 

 of the latter'-' (sec tiff. '.H\). Those lobes TOW rapidly, especially in length, and finally their tips 

 arch over until they meet. The edjros of the leaves coalesce, and thus is formed a globular 

 chamber above the original top of the ^onanu-ium. the walls of the chamber beino; composed of 

 the broad leaves which originated from the eduv of the bowl-like summit of the voting 

 "onanu-imu. In the meantime the ova in the blastostyle have arranged themselves in definite 

 groups, the largest yroup boino- the distal one, each jjrotip beino; now borne in a separate 

 gonophore, the gonophorea beino- arranged seriallv alony one side of the blastostyle. A tendency 

 toward such a o-rotipinof is seen in even (juito a yoiing gonophore (see lio-. '.>:,). The present 

 writer believes, from his study of Diphasia fallax. that Professor Allman was mistaken in two 

 particulars in his description of the u'onosome of />ijt}iiix!,t. First, in describing the develop- 

 mc'iit of the gonangiiun (of It. r<ix<i<;ii) that writer says: 3 



A lila^t'islylr ciccii|iics its axis, liavirii.' ii|mu its sMe-, mic ovrr the ntliL-r, the yminu' binMiiiLr u'"ii"i'ln ire.-, and 

 cx]ianiliii^ at its siuiiiiiit, intu a lima.l. tliick disk, whicli cluses, as with a ]I!HL'. tin- free end of the '_'<inai]'_'iinn. l']>cm 

 the (inter side of this disk a thin cliitiiinus invi'stini'iit is c'M-rrtrd, liecuniin^ << mliniiiins at the eilfic "f the 1 di>k with 

 tlie cliitinniis walls of the gonangium. 



This latter sentence coin'ey-. the idea that the end of the gonangium is fornieil subsequent 

 to the formation of the walls. As a matter of fact, it is entirely homologous with the 

 summit of other gonangia, and is continuous with the walls in the vomi^e-i ^onaie^ium that 

 I have been able to find (>ee li^'. !C5, which is a highly magnified view of a verv VOUIIL;' 

 gonangium}. In its earlv stages the gonangium of Diphasia f<ill<i.r is precisely similar to 

 all other e'onanyia, so far as this character is concerned. Kiy. iCi jiresents an appearance that 

 mijjht at first lead one to adopt Allman's view, as in this case the concave summit of the j^onan- 

 e-ium rests immediately on the deckenplatte. But when one studies a series of yoiing u'onan^ia 

 it becomes evident that we have here merely the elevation of the peripheral portion of the 

 gonangium top preparatorv to the growth of the leaves destined to form the marsupium. 

 Secondly. Professor Allman. after describing the acrocy.sts of several species, adds: 



In the rases ahuve desrrilied the acrnryst is destitute of any furl her niveriui;, and lias ils walls will] I heir irelati- 

 iii HI;- investinc'iit, freely ex|msed In the Surrounding water. In Xfrliilnriii nw/cfit. .V. fulln < . and N. I'luim-ism, however, 

 an additional covering is provided for the aemryst, and there is thus formed a rurioiis and rmn]iliraled rei-e|iiaelc\ in 

 which the ova, as in a sorl of iuarsii|iiuni, pass tlirmijrh certain early sla'je- of tlieir development, previously to lieiiii- 

 discharged into the siirronndiir.' water i p. ."int. 



'A monograph of the I iytniiolilastic or Tulnilarian 1 1 yd mid.-, London, ]s71. pp. 50 A 



-These lolies Allman very plausilily iiiterjirets as liein^ the limnologies of the lolmlar or sack-like processes 



which extend downward from the deckenplatte in Sertularia pumila. The derivation of the two structures i- evi- 



dently identical, and the only difference between them seems to In -in the dire. -lion of their growth, which is upward 

 in Diphasia fallax and downward in X rinl'irin /uniiilii. 

 :: i i\ tnnolilastic llydmids, lip. "ill M. 

 5125 PI 1' 04 - :} 



