178 ACTINT.T': OF AMJATIJOSS EXPLORATIONS M' MURRICH. 



a third cycle of Icn piiirs, all uoiioplioiic a loiiitli our ol' t\\('iity pairs 

 (Icstitutc of icpi'odiU'Mvc oiiians, and iii(li<;ali(nis in sonic cxoco'ls of a 

 liftli pair, Aviiicli is, liowi'vcr, inconiplclc Tlic incscntcrics arc thin, and 

 their inuseidature not very inaikedly dcvek>]i('d (I'l. xwiii, l^'i^. 71). 

 TIic acoidia are fairly luunerous and show alar_i;cdc\«']opnicnt of inland 

 cclls(IM. xxviii, Fis;-. If)). I'luM-onvcx snrfaccof an acoiitiiiinisoccnpicd 

 mainly by iicniatocysts, bclwtcn wliicli a. few scattered coarsely granu- 

 lar glaud cells occur, wliih^ iniincdiately below the ueniatocysts these 

 cells are very abuiulant, as tlicy likewise arc at the sides and towards 

 the concave surface. For the most part they stain dcepl}' Avith borax 

 carniine, though many — probably those in which the glandular i)roducts 

 are moi'c conipletely elaborated — lefnse to tak(> the stain and show a 

 yellow color. In one specimen I fonml the acontiai ]>i'otrnding fiom the 

 mouth, bjitcould not lind any emitted tiii'ongh the eoluniu wall, although 

 in sections through the wall line canals can be readily observed Avhicli 

 Inive no a])pearanee of being artefacts, and ])robably are einclidal. T 

 conld disroNcr no definite arrangement of these canals. 



There are three interesting features about this Sagartid: (1) Its 

 dceamerism. Tiiere are ten ])aiis of ])erfeet mesenteries, and the imper- 

 fect mesenteries are arranged sNinnictric ally to these ten, those of the 

 next subordinate cycle dcNcloping in (he exoeoels between adjacent 

 ])airs of jierfeet mesenteries. I ha\ e already snggested C*.*! ) that this (mmi- 

 dition probably aiises by llu^ suppression of a ]>air of mesenteries of the 

 ty])ical se<'ond <'yele, Sf> that this e\('Ie consists of four pairs oidy in- 

 sti'ad of six. Whether or not it is the same pair that is snpi»ressed in 

 each case in Avhich decamerism occurs can not be stated at present, hi 

 the decamerons llalcamj»ids it has Im-cii seen that it is the mesenteries 

 on eitluM- side of the snlcnlar dirtM-tixcs that have disai)peared,but it is 

 not impossible that in sporadic cases of decamerism, such as we have in 

 8. lactea, that it is the mesenteries on cither side of the sulcar directives 

 that have disa]>i>cared, or even the lateral mesenteries of the second 

 cycle. However that may be, it is certain, I think, that we must re- 

 gartl the ten pertect mesenteries of a decamerons form aseciuivalent to 

 the first and second cycles of a hexamerous ibrm. It follows from this 

 (2) that we have in ^'. lactea another instance of a Sagartid in which 

 more than the six ])rinniry mesenteries are i)erfect. llcrtwig (\S2) as- 

 sumed as a character of his family yagartiihc the jjrcsencc of only six 

 perfect mesenteries, which were also sterile, but von Heider ('77) had 

 already shown that there were numerous })crlcct mesenteries in ('<r<'iis 

 j)(<li(ii<iil(i(ii.s, and V. Dixon (\S8) has since shown that in those JSagar- 

 tias >\hich (loss(> considered typical species of the genus there are more 

 than six pairs of perfect mesenteries, it is ccrtaiidy a iact that the 

 majority of Sagartids whos«' anatomy we know possess only six pairs 

 of perfect mcscnt»'ries, but too nmny exceptions exist for this peculiar- 

 ity to be incbnled in the delinition <»f the genus. 3>nt not oidy does S. 

 lactea have the mesenteries of the second cycle perfect, but (o) the 



