346 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



slip has occurred in their delineation. Lastly, his crenated border (external 

 elastic coat) does not pass the constriction between the stylet-region and the 

 reservoir-region, whereas, as already shown, both this and the longitudinal coat 

 are continued some distance on the latter division. 



Reproduction of Proboscis. — So far as I am aware, no author has alluded to 

 the reproduction of this organ. The process was first observed in Ommatoplea 

 melanocephala, but it has since been seen in 0. gracilis, Tetrastemma algce, and 

 others. In a specimen of the former (0. melanocephala), from which three days 

 before the proboscis had been removed, there existed a pale conical papilla, 

 which projected a short distance behind the ganglionic commissures. Two days 

 after considerable progress had been made, and the organ proceeded backwards 

 as a slender rod tapered posteriorly (Plate VIII. fig. 1, a). There was a distinct 

 exterior coat from one end to the other, and an inner terminating at the com- 

 mencement of the posterior narrow portion. The former had a crenated edge in 

 contraction. The organ gradually increases in size and complexity, but continues 

 quite free posteriorly for a considerable time, until, indeed, the stylets are well 

 developed. At a further stage of growth (Plate VIII. fig. 2), the walls are defined 

 almost as in the complete structure, but of course are much more delicate and 

 plastic ; and the extreme contractility and elasticity of the entire organ are most 

 interesting, and raise a doubt as to the identity of its muscular fibres with those 

 of the higher invertebrates, since it so much surpasses them in mobility. The floor 

 of the anterior chamber ends in the usual pit, which is swollen on account of the 

 shortening of the organ. The walls of the muscular cavity behind the floor of the 

 anterior region are not well defined, though the space itself is large, and con- 

 tains a granular fluid. There is no central stylet, and the basal sac is repre- 

 sented by a somewhat triangular group of the usual granules, round which the 

 radiating fibres are placed. The wedge-shaped setting within the latter (fibres) 

 is mobile and translucent. A somewhat indistinct streak (/) in the central line 

 indicates the canal for the central stylet, and now and then this became bulged 

 by projected fluid. The lateral stylet-sacs, from the bulging of the chamber in 

 this instance, seem pressed backwards, but in reality they have their distinc- 

 tive position. Each contained a stylet or two, a few granules, and a clear 

 globule. 



The reservoir at this stage had assumed its characteristic shape, though its 

 glands were barely visible. The shortening and bulging of the anterior and pos- 

 terior chambers have annihilated the usual prominent appearance of this part, 

 and the last has encroached very much on the cavity posteriorly. The glands 

 were formed in the posterior chamber, though their contents were not elaborated, 

 and the cavity terminated in the usual cul-de-sac. A few rounded papillae at the 

 posterior end indicated the early condition of the muscular retractor or riband. 

 It is clear that at some time or other the latter becomes attached to the wall of 



