Prof. Allman on the Hydroid Zoophytes. 137 



XV. — Notes on the Hydroid Zoophytes. By Prof. Allman. 



I. Laomedea flexuosa, Hincks. 



In the polypes of Laomedea flexuosa, the ectoderm of the ten- 

 tacles is extended laterally between the^e organs for a distance 

 of about a fourth of their entire length from their origin, so as 

 to form a web-like membrane, similar to that already pointed 

 out by Mr. Alder in L. acuminata. 



This peculiarity in a very common zoophyte seems to have 

 been hitherto overlooked, though, in a morphological point of 

 view, it is a character of much importance. 



II. The cxtra-capsular medusiform sporosacs (" meconidia ") of 

 Laomedea, and the determination of the species in which they 

 they are found. 



In a communication on the Reproductive Organs of the 

 Hydroid Zoophytes, read last year before the Royal Society of 

 Edinburgh *, I referred to the extra-capsular medusiform sporo- 

 sacs, so well known from Loven's description of them in a zoo- 

 phyte which he names Campanidaria [Laomedea) geniculata, and 

 expressed my opinion that Loven's zoophyte was not truly Lao- 

 medea geniculata, but L. flexuosa of Hincks, a species to which 

 I referred similar bodies which I had myself examined. 



Mr. Alder, writing to me since then, suggests the possibility 

 of the species which gives rise to these sporosacs being neither 

 the one nor the other, but a distinct, though not yet discrimi- 

 nated, species. 



As we know that both L. geniculata and L. flexuosa give rise 

 also to a different kind of sexual bud, it will be at once seen 

 that this question has an important physiological significance 

 apart from its bearing upon simple descriptive diagnosis ; and 

 I therefore availed myself of the first opportunity to inquire 

 critically into the subject. The result has been a conviction 

 that Mr. Alder's doubts are well-founded. 



A few weeks since, I obtained upon the shores of Cramond 

 Island, in the Firth of Forth, a Laomedea, growing on the 

 fronds of Fucus vesiculosus, and loaded with gonophores, most 

 of which carried upon their summits the peculiar bodies under 

 consideration. 



The only described species of Laomedea with which it is pos- 

 sible to confound the Cramond zoophyte are L. flexuosa, L. ge- 

 niculata, and L. dichotoma. From L. flexuosa, however, it dif- 

 fers in the more elongated form of the polype-cells, in the more 

 conical form of the gonophores, and in the absence of the web 



* Proc. Roy. Soc. Edinb. 1858. 



