ON THE BLOOD -DISCS OF SIREN LACERTINA. 73 



existence of capsules, but of a lengthened shape, with fine long threads. 

 But these organs were much smaller and finer ; they had a remarkable 

 resemblance to the structures I described formerly as Spermatozoa of 

 the Actinia. A new investigation of the Actinite, as, for example, of 

 the Actinia cereus, convinced me that those structures formerly described 

 as Spermatozoa are nothing else but stinging threads of the Medusa ; 

 they stand closely studded round the feelers or arms, and on the exte- 

 rior surface. The threads project from long-shaped capsules, with 

 that remarkable movement which I have elsewhere described, and 

 which I found again precisely as formerly. The same organs, but only 

 in a different form, occur again in Polypi, as Ehrenberg and Dr. Erdl 

 (one of my companions) found in the Hydra ; and the latter discovered 

 them also in Veretillum. 



It is probable that the stinging has a mechanical and chemical 

 origin ; just as in the majority of what are termed poison-organs, we 

 find a liquid which collects in a little bladder or capsule, and an appa- 

 ratus capable of doing injury. So it is also with many stinging plants, 

 as the Loasete, in which fine sharp hairs convey a juice, where circula- 

 tion can be so beautifully observed. 



More extended researches regarding these structures, provisionally 

 considered as stinging organs, will make known much that is remarkable 

 in reference to their occurrence, arrangement, structure, and move- 

 ments, and will display great riches in respect to phenomena of organi- 

 zation. . 



XIV. ON THE BLOOD-DISCS OF SIREN LACERTINA.* 



By Professor Owen, F.R.S., #c. 



AMONG the important generalizations which the numerous observations 

 of recent microscopical anatomists have enabled the physiologist to 

 establish, respecting the form and size of the blood-discs in different 

 classes of animals, the most interesting seems to be that which Pro- 

 fessor Wagner has enunciated respecting the relation of the magnitude 

 of the blood- disc to the persistence of the branchial apparatus in the 

 Batrachian order of Reptiles, on the occasion of his description of the 

 blood- discs of the Proteus anguinus. 



* Extracted from the Penny Cyclopedia, Art. Siren, Sept. 25th, 1841. 



