564 



MKRISTIC VARIATION. 



[PART i. 



to below, in evidence that the total number of cases is considerable. 

 There are only two certain cases of double head (see Ti/]>*////ix, Xo. 868, 

 and Allolobophora, No. 873). 



POLYfll.l.TA. 



*S68. Typosyllis variegata : individual having two small heads, as 

 shewn in Fig. 208. Heads of unequal size, that on the left having 4 

 segments behind the eyes, while that on the right had two. The 



869. 



870. 



871. 

 S7:.'. 



I'm. 20><. 'l'yi><ixylli.-i riii-ii'i/ntd. No. 8G8, having two small heads. 

 (After LANQEKHANS.) 



appearance suggested that the original head had been broken off and 

 that two new ones had uruwn in its place. LAXGEUIIANS, P., J~m 

 Acta Ac. C. L. C., XLII. p. 102, I'l. 



Nereis pelagica : liilid posteriorly. BELL, F. JEFFREY, Proc. Zool. Soc., 188G, p. 3. 



Salmacina incrustans (Serpulidse) : posterior end double. [Two tails shewn in 

 figure as of equal length and in the same straight line, at ri^ht angles to the body. 

 The arrangement of the segmentation at the junction is not clearly shewn.] 

 CLAi'AuV.i'K. MI ni. mx-.jilii/is. t't tl'liiat. mil. (ii'iif-i-f, xx. 1869 70, p. 177, PI. xxx. tig. ~> v. 



Proceraca tardigrada (Syllida ) : tail double; two specimens. In one of these 

 the tails were nearly equal, but one had no anal cirri. AXIUIKWS, E. A., l'ri-. I'. 8. 

 Xut. Mua., is'.H; x*iv. p. -is:;, and Amer. Xt., isii-J. xxvi. p. 7'2'.i, PI. xxi. 



Branchiomma sp. (Sabellidse) : two pnstcrior ends, out 1 In'iwj rudimentary. 

 IlKiM/u T:, Trav. Xtnt. Zool. de (.',!{,. isss, p. S [inioted from AXDKEWS, /. c.] 



[With these conditions compare Si/llia r<iin*ii, a form found by the ('Imlli'iiiii-i- 

 in tw localities, inhabiting a Hexactinellid Sjionge. The body of this creature con- 

 sisted of vast numbers of branches, abontas thick as thread, passing off at right angles, 

 coiling upon each other and forming inextricable masses. In some specimens no 

 head was found, but a single head was afterwards discovered. It seemed likely that 

 large tracts of the body have no head, but there was no evidence to shew how many 

 heads occur in the colony. Many female buds were found, and a single complete 

 male. Mclxxosn, Chull. Jli'i>., xn. p. I'.l*. I'l. xxxi.] 



