CHAP, xvi.] RADIAL SERIES : JELLY-FISH. 425 



*G31. Sarsia sp. Among many thousands examined on the east 



coast of Scotland one was found having six radial canals, six 



ocelli and six tentacles. ROMANES, O. J., Join: Linn. $oc., Zool., 



xn. p. 527. 

 *632. Sarsia sp. A single specimen having Jive complete segments: 



the only abnormality met with among thousands of naked-eyed 



medusae observed, ibid., xm. p. 190. 



There is perhaps in the whole range of natural history no 



more striking case of the Discontinuity and perfection of Meristic 



Variation. 



Is it besides a mere coincidence, that the specimens presenting 



this variation, so rare in the free-swimming Hydromedusse, should 



have been members of the same genus ? 



633. Clavatella (Eleutheria) prolifera. This form has a medusa 

 which creeps about on short suctorial processes borne by the tentacles. 

 The number of these tentacles varies from 5 to 8. In the specimens 

 examined by KROHN' the number was 6. Most of CLAPAREDE'S* speci- 

 mens had 8. FiLiPPi 3 found that the majority had 6 arms, but 15 per 

 cent, had 7. Those examined by HiNCKS 4 never had more than 6. 

 Filippi considered that the difference in number was evidence that his 

 specimens were of a species different from Claparecle's. I examined 

 many of this form at Concarneau and found six the commonest number 

 in the free medusas, but those still undetached frequently had 5, 

 possibly therefore the number increases with development. [See also 

 Cladonema radiatum, &c. HINCKS, I.e., p. 65, &c.] 



Claparede states that the 6-armed specimens had 6 radial canals, 

 but the 8-armed usually had four though occasionally six, but never 

 eight canals. 



In this case note not only the frequent occurrence of Meristic 

 Variation, but also the suggestion that particular numbers of tentacles 

 are proper to particular localities. 



*634. Normally there is a single eye at the base of each arm. CLAPAREDE 

 figures (I.e. p. 6, PL i. fig. 7 a) a case of duplicity of an eye, and says 

 that specimens occur in which each eye is doubled, so that there are 

 two eyes at the base of each arm instead of one. 



635. Stomobrachium octocostatum ( JEquoridse) : variety found in 

 Cromarty Firth, frds of size represented by FORBES (Monogr. Br. 

 Naked-eyed Jfedusce) ; ovaries bluish instead of orange, and without 

 denticulated margins. Tentacles arranged in double series, long and 

 short alternating, while in the type the series is single. The number 

 of large tentacles same as in type. Each smaller tentacle bears vesi- 

 cular body at base, without pigment or visible contents. The same 

 variety figured by EHRENBERG, Abh. Ak. erl., 1835, Taf. vm. fig. 7. 

 ROMANES, G. J., Jour. Linn. Soc. xn. p. 526. [Simultaneous Variation 

 of the several segments.] 



With Nos. 634 and 635 compare the fact that in. Tiarops poly- 



1 Arch.f. Naturg., 1861, p. 157. 



2 Beob. iib. Anat. u. Entw. Wirbelloser Thiere, 1863, p. 5. 



3 Mem. Ac. Torino, S. 2, xxm. p. 377. 



4 Brit. Hyd. Zoophytes, 1868, p. 71. 



