34 



NATURAL SCIENCE. 



July, 1893. 



but faint — a slight rounded swelling at the apex — with presence of 

 a few of the ordinary nematocysts of the tentacles. From this stage 

 there were all gradations up to a few rare instances where the apex 

 of the c.-cystophore bore a perfect capitate tentacle precisely the same 

 in structure to the normal tentacle, saving that the stalk was extremely 

 short, just equal in length to the diameter of the head. All the 

 examples of this variation were furnished by the lot gathered in June. 

 The proportion was surprising. Out of 118 specimens examined but 

 40 were without thi abnormality in the c.-cystophores. 



14 showed one colleto-cystophore with tentacle-crowned apex. 



15 ,, two 

 15 ,, three 



four 



five 

 six 



seven 

 all the 



Otherwise these specimens showed but little mutability. Two 

 colleto-cystophores were doubled and one specimen had an extra 

 group of tentacles, while another lacked one. 



In the larger specimens taken earlier in the year, the tentacle- 

 crowned c.-cystophore phase was not observed, but there was extreme 

 want of symmetry. Quite 33 per cent, showed variation in the number 

 of colleto-cystophores or in the groups of tentacles. The greater number 

 (more than half) were cases where the marginal organ was wanting 

 in the space where normally it would be found ; the others were 

 instances of excess number of tentacle groups (accompanied usually 

 by the presence of an equal number of excess colleto-cystophores) or 

 of duplication — " twinning " — of one or two of the last-named bodies. 



The conclusions to be drawn from the last mentioned abnor- 

 malities are obscure, but those where the colleto-cystophores bear the 

 papillate appendix at the summit are certainly atavistic, explainable 

 by the original derivation of these organs from ordinary papillae. 



James Hornell. 





