Prof. Allman on the Hydroid Zoophytes. 139 



which give origin to cxtra-capsular medusiforni sporosacs; as 

 yet, however, we have no evidence of any other than that here 

 described. Though Lister is the first author who has spoken 

 of the remarkable bodies in question, having figured male 

 examples of them in the paper referred to, yet it is to Loven we 

 are indebted for the first accurate and full description of them. 

 I have therefore thought it right to dedicate the present species 

 to the Danish naturalist whose name has already become in- 

 timately associated with these medusiforni sporosacs, and to 

 designate it as Laomedea Loveni. 



In the paper above referred to, I mentioned my having failed 

 to detect in the cxtra-capsular sporosacs, whether male or female, 

 any trace of the radiating canals first described by Loven. In 

 my more recent examination of these bodies, I was for a long- 

 time, notwithstanding the most careful scrutiny, equally unsuc- 

 cessful ; but at last a specimen occurred, with female gonophores, 

 in which the appearance figured by Loven was not only apparent 

 but strikingly obvious. I am still, however, of opinion that 

 this peculiarity of structure is not constant, many specimens 

 presenting not the slightest trace of it. 



The real meaning of these rib-like lines is, after all, a matter 

 not easily settled. They may be proper tubes, the true repre- 

 sentatives of the. radiating canals of a Medusa; but there seems 

 at least equal reason to consider them as mere folds of a mem- 

 brane which lies immediately within the ectothecal covering 

 of the sporosac, and I confess myself unable to give a decided 

 opinion on this point. In favour of the former view may be 

 adduced their undoubtedly tube-like appearance, their occurrence 

 in fours, and the fact that their presence would be quite in 

 accordance with what analogy would lead us to expect. On the 

 other hand, against their being gastro-vascular canals may be 

 urged their obliteration under slight pressure, the absence of all 

 trace of motion in their interior, and, above all, their frequent, 

 if not most usual, non-existence. 



The opportunities I have just had of examining these extra- 

 capsular sporosacs have enabled me to determine their exact 

 structure more fully than appears to have been yet done. I 

 now find that three separate membranes enter into the compo- 

 sition of their walls. Most internally is a membrane which 

 immediately confines the ova or spermatozoa, and which was 

 originally the ectodermal layer of the manubrium. This invest- 

 ment is generally of short duration, becoming absorbed or 

 ruptured under the increasing volume of the generative products. 

 It is the endotheqae, according to the terminology I have already 

 ventured to propose (Proc. Royal Soc. Edin. Dec. 1858). Most 

 externally is a thick ectodermal layer loaded with thread-cells 



