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- 

 grain. Tliough 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 open'ng in the extremity of the spine. On 

 the other hand, the sac could be easily lilled 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 tlie sac, whilst on the 

 left-hand side there is only a small opening instead of the tube. Tlie attempts to 

 introduce a bristle into this opening for any distance failed, as it appears to lead into 

 tlie interior of the basal portion of the operculum, to which the sac flrmly 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. 



Tlius 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 liaAe been modified into poison-organs, and the 

 actual communicaticjn 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 liope 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. 

 Tlie 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 tlie speci- 



