438 DR. GUNTHER ON THE FISHES OF CENTRAL AMERICA. 
base of the spine, entering into a sac situated on the opercle and along the basal half 
of the spine; the sac is of an oblong-ovate shape, and about double the size of an oat- 
erain. Though the specimen had been preserved in spirits for about nine months, it 
still contained a whitish substance of the consistency of thick cream, which on the 
slightest pressure freely flowed from the opening in the extremity of the spine. On 
the other hand, the sac could be easily filled with air or fluid from the foramen of the 
spine. 
No gland could be discovered in the immediate neighbourhood of the sac; but on a 
more careful inspection I found a minute tube floating free in the sac, whilst on the 
leftehand side there is only a small opening instead of the tube. The attempts to 
‘ntroduce a bristle into this opening for any distance failed, as it appears to lead into 
the interior of the basal portion of the operculum, to which the sac firmly adheres at 
this spot. 
2. The dorsal part is composed of the two dorsal spines, each of which is 10 lines 
long. ‘The whole arrangement is the same as in the opercular spines; their slit is at 
the front side of the point; each has a separate sac, which occupies the front of the 
basal portion ; the contents were the same as in the opercular sacs, but in somewhat 
greater quantity. A strong branch of the lateral line ascends to the immediate 
neighbourhood of their base. 
Thus we have four poison-spines, each with a sac at its base; the walls of the sacs 
are thin, composed of a fibrous membrane, the interior of which is coated over with 
mucosa. ‘There are no secretory glands imbedded between these membranes, and these 
sacs are probably merely the reservoirs in which the fluid secreted accumulates. The 
absence of a secretory organ in the immediate neighbourhood of the reservoirs (an organ 
the size of which would be in accordance with the quantity of the fluid secreted), the 
diversity of the osseous spines which have been modified into poison-organs, and the 
actual communication indicated by the foramen in the sac, lead me to the opinion that 
the organ of secretion is either that system of muciferous channels which is found in 
nearly the whole class of fishes, and the secretion of which has poisonous qualities in a 
few of them, or at least an independent portion of it, 
This description was made from the first example; through the kindness of Capt. Dow 
I received two other specimens; and in the hope of proving the connexion of the poison- 
bags with the lateral-line system, I asked Dr. Pettigrew, of the Royal College of Surgeons, 
a gentleman whose great skill has enriched that collection with a series of the most 
admirable anatomical preparations, to lend me his assistance in injecting the canals. 
The injection of the bags through the opening of the spine was easily accomplished ; 
but we failed to drive the fluid beyond the bag, or to fill with it any other part of 
the system of muciferous channels. This, however, does not disprove the connexion of 
the poison-bags with that system, inasmuch as it became apparent that, if’there be 
minute openings, they are so contracted by the action of the spirit in which the speci- 
