ON THE BRITISH ANNKLIDA. 263 



The succeeding stage (5) is marked by a still further development of this 

 curved line of cells. At a subsequent phase (6) these cells assume the un- 

 questionable character of young worms having the power of independent 

 motion while yet in the midst of vitelline mass. What is remarkable is, that 

 the ovum, while the young is thus being evolved, undergoes a great increase 

 of size. This can only occur by absorption of nutrient fluid from without. 



At(b"", fig. 68) the inferior uterine duct, it will be seen that the young 

 escape out of the ova before they finally leave the parent, and that they are 

 endowed with independent capabilityof locomotion ; 7,8,9, 10, fig.71, illustrate 

 the minute anatomy of the young at this stage (intra-uterine) of growth. 

 Minute groups of molecules are first seen (7) in the axis of the body, which 

 subsequently become fused (8) into a continuous series, in which it is im- 

 possible to discern a channel. At another age, however, a distinct intesti- 

 nal canal (9) appears ; this is surrounded on either side by a longitudinal 

 row of cells which indicate the future blood-vessels. Still further developed 

 (10), this canal exhibits incipient evidences of segmental contractions; and 

 what should be expressly noted, the interval between the intestine and inte- 

 gument becomes filled with a fluid, already corpusculated, the motions of 

 which may be distinctly and unmistakeably discerned. Thus the physiologist 

 has attained to a knowledge of one definitive /ac< in relation to the embryo- 

 logical history of the chylo-aqueous fluid of the peritoneal cavity of the An- 

 nelida, that it begins its functions in the embryo before the true-blood. This 

 latter is a system of subsequent development. So simple is the first stage of 

 nutrition that it is accomplished exclusively by the chylo-peritoneal fluid. 

 It may be here affirmed (what may hereafter prove to be embryologically 

 true of all worms, and probably of all articulated animals) of the Earth-worm, 

 that the younger the individual the greater the volume of the chylo-perito- 

 neal fluid, the older the less ; the proportion of this fluid, in other words, is 

 inversely as the age. It is thus established by actual demonstration, that the 

 Earth-worm is viviparous, and that it is hermaphrodite and self-impregnating, 

 although only under the condition of being united to another individual. 



Illustrations of the generative organs of Nais Jiliformis adorn the pages of 

 almost every systematic work on comparative anatomy, published since the 

 date of the researches of M. Duges. Each author in long succession, as usual, 

 adopts reverently the original of M. Duges ; where he is wrong they are 

 wrong, where right they are so. The researches of M. Duges into the ana- 

 tomy of the generative system of this little worm constitute undoubtedly his 

 master-performance in minute investigation. At the period of his inquiries 

 it was by no means easy to unravel the reproductive organs of Nais. Itself 

 of microscopic minuteness, it demands the use of the highest and the clearest 

 powers, and that too in a living specimen, ceaselessly in motion, that the 

 problem may be satisfactorily solved. The descriptions amount to a credit- 

 able approximation to the results obtained through aid of the best modern 

 microscope *. They are notwithstanding deficient, in respect that they 

 omit all allusion to parts which are indispensable to the sexual system as a 

 whole. 



A comparison of the familiar figures of Duges with those which are pub- 

 lished for the first time in connexion with this Memoir, will enable the phy- 



* Nearly two months of my time were almost exclusively devoted to the study of the re- 

 productive organs of Nais filiformis. During this period thousands of separate individuals 

 were submitted to dissection. It was only in one, now and then, that those developed con- 

 ditions of the sexual system could be found, which were essential to the success of the inquiry. 

 There is, therefore, every excuse for inacciuacy. 



