40 
THE POLYPI. 
$ 28. 
These poisonous and prehensile organs are destroyed by use, which is 
_also true of the nettling organs. 
speedy reproduction. 
But this loss is probably repaired by their 
This last circumstance may explain the various 
descriptions given them by different authors, for, probably they have been 
observed at dissimilar stages of development. ? 
8 Erdi, who has discovered a great number of 
these nettling organs, saw, in some cases, the thread 
directly continuous with the neck of the vesicle ; in 
others, these necks appeared furnished with spines 
directed backwards; exactly as Wagner had 
before described, and as Kélliker had often ob- 
* [§ 28, note 3.]. These nettling organs of the 
Polypi have recently been very successfully studied 
‘by Agassiz, 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 exhausting 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. AsI have also studied these forms, I will 
ase my own language, in the description of what 
Prof. Agassiz has seen. There are several varieties 
of these cells or capsules, depending upon the ar- 
vangement and structure of the lasso ; sometimes 
this last is a simple ooil, sometimes it is coiled about 
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 cases, the essential feature of these organs is the 
Jasso 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, 
4n internal instead of an external cilium, coiled 
up ina 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). 2rdi asks if these variations 
of ‘form are not coincident with an increasing or 
decreasing activity of the sexual organs (see 
Muller’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”), Pl. 
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 igs 
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 Radiata 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 Mollusca, and although their 
general structure is the same, there are points of 
difference of even a zoological value. 
Epiror. 
