ft 



■104 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



proboscis had been ejected. The ova are deposited from the beginning of February 

 till June; sometimes adhering together in irregular masses by their edges or a 

 little accidental mucus, at others scattered about the vessel in detached groups. 

 In several instances, however, they were deposited in a translucent sheath of 

 mucus. On deposition they have the aspect shown in Plate XIII. fig. 3, being of 

 a granular structure throughout, with a clear spot and globule, and measuring 

 about xioth °f an mcn m diameter. The ova pass rapidly through the usual 

 stages, and on the 11th of February the embryos were revolving rapidly in the 

 egg by aid of their cilia, and in some cases hatched. The extruded animal (Plate 

 XIV. fig. 3), under moderate pressure, has a globular form, but assumes various 

 shapes when freed — the ordinary one being that of an apple — the long ciliary 

 process representing the stalk, while the body slightly tapers towards the 

 posterior end. It revolves rapidly between the glasses. The body is opaque and 

 granular, with the exception of the margin, which is somewhat paler, from the 

 slight differentiation of the cutaneous textures. Externally, it is coated with 

 long cilia, by aid of which it executes rapid motions, and a tuft anteriorly had 

 the form of a long whip-like process, as during the progress of the animal it 

 appeared like a single mobile thread. The body is sometimes pitted at the origin 

 of the latter, while a slight papilla projects at the posterior end. When fixed 

 between the glasses the cilia were soon pitched off, and the animal resolved itself 

 into a number of cells and granules (Plate XII. fig. 11). In two days the animal 

 is found somewhat elongated (Plate XIV. fig. 4), and the mouth (a) becomes more 

 evident as a strongly ciliated slit placed nearly in the centre of the body, which, 

 with the above-mentioned exception, is still uniformly granular. A longer tuft 

 of cilia at the anus is now more distinctly seen. Two days later considerable 

 increase has occurred in the length of the body (Plate XIV. fig. 5), and from the 

 more anterior position of the mouth, it is apparent that the chief increment has 

 taken place in the posterior region. The outline is now pear-shaped, the snout 

 being much less tapered than the tail. The cutaneous textures are more distinctly 

 marked, and the cells, with their refracting contents, very apparent ; there is also 

 a corresponding advance in the growth of the granules of the alimentary canal, 

 its ciliation, and the posterior sacculations. The whip-like tuft of cilia on the 

 snout is somewhat shorter, and there now exist a few longer cilia on the side of 

 the head, the posterior group of which (c) are evidently the precursors of the long 

 ciliary tuft, which by-and-by appears. There is as yet no trace of eye-specks. A 

 few cylindrical papillae are observed on the snout and tail, and one or two along 

 the sides, which processes do not seem to result from pressure. In a day or two 

 afterwards some are furnished with one and others with two eye-specks. More- 

 over, the tuft of cilia on the snout is gradually diminishing in length, while the 

 lateral cilia (c) before-mentioned are becoming longer. During a period stretch- 

 ing from March to the beginning of June, the various vessels swarmed with 



