EMBRYONIC DEVELOPMENT OF PURPURA. 617 



takes -place very rapidly ; the ciliated lobes are much more highly 

 developed, being extended in a long sinuous margin, so as almost 

 to remind the observer of the 'Wheels' of Rotifera (§ 354), and 

 being furnished with very long Cilia (Fig. 325, b) ; the Auditory 

 Vesicles, the Tentacula, the Eyes, and the Foot, successively make 

 their appearance ; a curious rhythmically- contractile Vesicle is 

 seen, just beneath the edge of the shell in the region of the neck, 

 which may, perhaps, serve as a temporary heart ; a little later, 

 the real Heart may be seen pulsating beneath the dorsal part of 

 the shell ; and the mass of yolk-segments of which the body is 

 made-up, gradually shapes itself into the various organs of Di- 

 gestion, Respiration, &c, during the evolution of which (and 

 while they are as yet far from complete) the Capsule thins-away at 

 its summit, and the Embryoes make their escape from it.* 



480. It happens not unfrequently that one of the Embryoes 

 which a Capsule contains does not acquire its Supplemental Yolk 

 in the manner now described, and can only proceed in its develop- 

 ment as far as its original yolk will afford it material ; and thus, 

 at the time when the other embryoes have attained their full size 

 and maturity, a strange-looking creature, consisting of two large 

 ciliated lobes with scarcely the rudiment of a body, may be seen 

 in active motion among them. This may happen, indeed, not only 

 to one but to several Embryoes within the same Capsule, especially 

 if their number should be considerable ; for it sometimes appears 

 as if there were not food enough for all, so that whilst some attain 

 their full dimensions and complete development, others remain of 

 unusually small size, without being deficient in any of their organs, 

 and others again are more or less completely abortive, — the supply 

 of supplemental yolk which they have obtained having been too 

 small for the development of their Viscera, although it may have 

 afforded what was needed for that of the Ciliated Lobes, Eyes, Ten- 

 tacles, Auditory vesicles, and even the Foot, — or, on the other hand, 

 no additional supply whatever having been acquired by them, so 

 that their development has been arrested at a still earlier stage. — 

 These phenomena are of so novel and remarkable a character, that 

 they furnish an abundant source of interest to any Microscopist 

 who may happen to be spending the months of August and Sep- 

 tember in a locality in which the Pwpura abounds ; since, by 

 opening a sufficient number of Capsules, no difficulty need be expe- 

 rienced in arriving at all the facts which have been noticed in this 



* The Author thinks it worth while to mention the method which he 

 has found most convenient for examining the contents of the Capsules 

 of Purpura ; as he believes that it may be advantageously adopted in 

 many other cases. This consists in cutting-off the two ends of the cap- 

 sule (taking care not to cut far into its cavity), and in then forcing a jet 

 of water through it, by inserting the end of a fine-pointed Syringe (§ 101) 

 into one of the orifices thus made, so as to drive the contents of the cap- 

 sule before it through the other. These should be received into a shallow 

 cell, and first examined under the Simple Microscope. 



