DEVELOPMENT OF PURPUEA 939 



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 Kotifera, and being furnished with very long cilia (fig. 

 713, 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 digestion, respira- 

 tion, etc., during the evolution of which (and while they are as yet far 

 from complete) the capsule thins away at its summit and the embryos 

 make their escape from it. 1 



It happens not imfrequently that one of the embryos which a 

 capsule contains does not acquire its ' supplemental ' yolk in the 

 manner now described, and can only proceed in its development as far 

 as its original yolk will afford, it material ; and thus, at the time when 

 the other embryos 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 embryos 

 within the same capsule, especially if their number should be con- 

 siderable ; 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, tentacles, auditory vesicles, and even the 

 foot or, on the other hand, 110 additional supply whatever having 

 been acquired by them, so that their development has been arrest i < 1 

 at a still earlier stage. These phenomena are of so remarkable a 

 character that they furnish an abundant source of interest to any 

 microscopist who inav happen to be spending the months of August 

 and September in a locality in which the I'ln-fmra abounds ; since, 

 by opening a sufficient number of capsules, no difficulty need be 

 experienced in arriving at all the facts which have been noticed in 

 this brief summary. 2 It is much to be desired that such microscopists 



1 The Author thinks it worth while to mention the method which he has found 

 most convenient for examining the contents of the egg-capsules of Pn rjni r</, as .he 

 believes that it may be advantageously adopted in many other cases. This consists 

 in cutting off the two ends of the capsule (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 into one of the orifices thus made, so as to drive the contents of the capsule 

 before it through the other. These should be received into a shallow cell and first 

 examined under the simple microscope. For some further observations on the de- 

 velopment of Piayjiira, see Professor Haddon, ' Notes on the Development of the 

 Mollusca,' Quart. Ju/ini. M/crosr. Sri. xxii. p. 3t>7. 



- Fuller details on this subject will be found in the Author's account of his re- 

 searches in Trillin. Mirror-, tioc. ser. ii. vol. iii. 1855, p. 17. His account of the 

 process was called in question by MM. Koren and Danielsseu, who had previously 

 given an entirely different version, of it, but was fully confirmed by the observations 

 of Dr. Dvster. 'See Ann. Xat. Hist. ser. ii. vol. xx. 1857, p. 1C. The independent 



