332 DR w. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



Under a high power (700-1000 diam.), the moving bodies appear as mere specks 

 or points, and they retain this remarkable motion for upwards of twenty-four 

 hours after extrusion from the cavity into the surrounding salt water. There is 

 thus a peculiar fluid rich in these granules secreted by the posterior chamber or 

 gland ; and continued observation, and the whole anatomy of the parts, show that 

 this fluid passes forwards into the reservoir, where it is probably mixed with a 

 small quantity of another secretion from the glandular walls of the latter, and 

 then propelled with force through the ejaculatory duct into the anterior chamber. 

 What its peculiar function in the anterior chamber, or when discharged into the 

 surrounding medium in the extruded state of the parts, may be, can only be con- 

 jectured at present; but from the elaborate structure of the parts concerned in 

 its economy its action would seem to be important. I have no observations in 

 support of the view that this granular fluid is poisonous. It cannot pass into a 

 wound at any rate until the stylet is withdrawn ; and if it really acts as a poison 

 to animals when introduced into their tissues, it might reasonably be supposed 

 to affect them injuriously when discharged into the water around them. Whether 

 the fluid has any influence on the secretion of the stylets in the lateral sacs, or in 

 the central apparatus, I am unable to say ; but, as already mentioned, a minutely 

 granular fluid has been seen in the former, and a large though imperfect stylet 

 in the posterior chamber of O.pulchra. MM. de Quatrefages, Van Beneden, and 

 others, state that the proboscis and the foregoing apparatus are used in attacking 

 prey ; but, we may ask, Do the Borlasians use their feeble and unarmed structure 

 for the same purpose? So far as I have seen, the proboscis is a somewhat pre- 

 carious aggressive weapon, since it frequently adheres to the attacking body, and 

 is thrown off. It is true we may assign, with an air of probability, an aggressive 

 function to the central stylet ; but we cannot do so with the very same organs 

 in the lateral sacs ; for, being developed in a free condition within almost closed 

 cavities, they are quite useless as offensive weapons. 



In extrusion of the proboscis (Plate VI. fig. 2), the entire spike of the stylet 

 projects, the floor of the anterior chamber forms all round a thick and powerful 

 umbrella-shaped cushion (whose independent structure has escaped Prof. Kefer- 

 stein), the lateral stylet-sacs are under cover, and the region of the reservoir is 

 shortened and widened. The position of the muscular chamber (e), which forms 

 a second small umbrella round the apex of the basal sac of the central stylet, has 

 already been mentioned. The separation between the longitudinal fibres of the 

 stylet-region proper (v) and the looping fibres (t) of the reservoir is well marked 

 in this condition. It will also be observed that the stylet-region is widened 

 by the forcible wedging forwards of the reservoir. 



The walls of the posterior chamber, after forming the cul-de-sac, are continued 

 backwards in the form of one or two long translucent muscular ribands of extreme 

 flexibility and contractility (\|/-, fig. 4, Plate VIII.), and which are attached to the 



