40 



THE POLYPI. 



^28. 



These poisonous and prehensile organs are destroyed by use, which is 

 also true of the nettling organs. But this loss is probably repaired by their 

 speedy reproduction. This last circumstance may explain the various 

 descriptions given them by diiFerent authors, for, probably they have been 

 observed at dissimilar stages of development.''" 



3 ErdI, who has discovered a great number of 

 these nettliiif; organs, saw, in some cases, the thread 

 directly continuous with tlie neck of the vesicle ; in 

 others, tliese necks appeared furnished with spines 

 directed backwards ; exactly as fVai^ner had 

 before described, and as KolUker had often ob- 



* [§28, notes.] These nettling organs of the 

 Polypi have recently been very successfully studied 

 by Agansiz, who has enjoyed the most enviable 

 advantages with the Polypi and Acalephae of the 

 North American coast. He has changed the entire 

 aspect of the subject, besides almost exhaustmg it for 

 future research. His special studies were made on 

 the coral polyp of our southern coast, the Astrangia 

 Danae, Agass. The complexity of structure of 

 these lasso-cells, as he has very appropriately 

 termed them, is truly wonderful for such minute 

 forms. As I have also studied these forms, I will 

 use my own language, in the description of what 

 Frof. Agassiz has seen. There are several varieties 

 of these cells or capsules, depending upon the ar- 

 rangement and structure of the lasso ; sometimes 

 this last is a simple ooil, sometimes it is coiled about 

 a staff which is erected from the base, but which is 

 also a part of the projectile apparatus. In the first 

 case, the lasso is much the longer and may be fifty 

 or seventy-five times the length of the vesicle; while, 

 in the second case, it rarely exceeds the length of 

 this last by more than sixteen or twenty times. In 

 all casps, the essential feature of these organs is the 

 lasso or internal coil, which is of a most curious 

 structure. In the first place, it is, in general terms, 

 only an inverted portion of the vesicle or cell itself, 

 an internal instead of an external cilium, coiled 

 up in a regular manner. When thrown out, there- 

 fore, it is wholly inverted, and its projection consists 

 . of an instantaneous turning of the whole inside out. 

 But the lasso, delicate as it is, has still more delicate 

 structures on its surface. These consist of barbels 

 arranged in regular spiral rows, which extend 

 to the very extremity of the lasso. At this last 



served (Beitrage z. Kenntniss d. Geschlechtsver- 

 haltnisse u. d. Samenfliissigkeit wirbelloser Thiere, 

 1841, p. 44, fig. 14). Erdl asks if these variations 

 of form are not coincident with an increasing or 

 decreasing activity of the sexual organs (see 

 MuUer's Arch. 1842, p. 305). * 



point, they almost elude the highest and best micro- 

 scopic powers. These barbels all point backwards 

 when the lasso is extended, and serve, no doubt, as 

 teeth, to prevent it from slipping on the objects over 

 which it is thrown. But these most delicate struc- 

 tures, which in beauty transcend that of all other 

 tissues, can be better appreciated by figures than 

 by the most minute description ; see Agassiz's 

 Memoir on Astrangia Danae (forthcoming in the 

 "Smithsonian Contributions to Knowledge"), PI. 

 VI. These observations, however, were made in 

 1848 ; see Proceed. Amer. Assoc. Advancem. Sc. 

 1848, p. 68. 



From my own observations there would, indeed, 

 be nothing to add on the special points studied 

 by Agassiz ; but a remark or two may be made as 

 to the development of these forms. 



The lasso-vesicle is, originally, only an epithelial 

 cell, of a spheroidal shape. It soon elongates, its 

 contents become cloudy, after which, the coil is 

 seen, very faintly marked, lying on the inner wall. 

 It would seem probable, therefore, that its forma- 

 tion was somewhat similar to that of the spiral 

 vessels in plants, although it is true that the lasso- 

 coils and these spiral vessels are analogous only in 

 form and position, and not in structure. The details 

 of the formation are unknown. 



These lasso-cells are more widely distributed 

 among the Kadiata than hitherto supposed. Agas- 

 siz (as he has informed me by letter) has observed 

 them on most of the Polypi and Acalephae, and even 

 with some of the MoUusca, and although their 

 general structure is the same, there are points of 

 difference of even a zoological value. 



Ebitob. 



