250 REPORT— 1851. 



escape from the ovarian system into the free space of the peritoneal cavity, 

 wherein they sojourn until the next phase of their growth has been attained. 

 It is during the period marked by the presence of true ova in the chamber 

 of the peritoneum, floating in the contained fluid, that the division of the 

 body of the parent animal takes place. In each fragment is nestled, incu- 

 bated, a considerable number of ova. Filled still by the fluid of the perito- 

 neal cavity, each fragment becomes subservient to the end of hatching the 

 young. It resists decomposition only for the period required for the ac- 

 complishment of this purpose. When the ova are committed to the sand, 

 the fragment rapidly disappears by putrefaction. The fission of the body, 

 thus interpreted, becomes the last act of the parental worm, since the portions 

 into which the body is subdivided by fission, never take food. The proboscis 

 of the cephalic fragment is never more protruded to take in sand. With the 

 fission the necessity for food terminates. If, on the contrary, the division of 

 the body were the first step of a real reproductive operation, characterized 

 by the superaddition of new segments to the body, the reconstruction of lost 

 heads, and the manufacture anew of departed tails, a resort to physiological 

 arguments were little required to prove that each fragment should grow vo- 

 racious, and consume extra supplies of nourishment, in order to provide the 

 necessary pabulum for the reparation of the mutilated parts. As this is not the 

 fact, the inference is clear that the division of the body is not the prelude to 

 a series of reconstructive operations by which parts are made " wholes," or 

 mutilations repaired. The experiment of artificially bisecting the body of a 

 Nereid or an Earth-worm, replacing the divided halves with care again in 

 their native habitats, invariably, in the author's hands, has led to the follow- 

 ing results. 



The cephalic half, by this division of the body, does not lose the power of 

 locomotion. In a few days after the operation it begins to grow less active 

 and vigorous in its movements ; the annulus at the point of division begins 

 to contract and wither ; in process of a few more hours it dies — it mortifies 

 away. This process of dissolution creeps in the direction of tlie head from 

 one segmental ring of the body to the other, until finally the cephalic remnant 

 ceases to manifest any signs of life. 



The tail-half immediately loses the power of advancing; it writhes on one 

 spot, and that only on contact of some external body ; its motions become 

 excited, not voluntary ; it never reacquires the power of swallowing earth. 

 The process of decay begins much sooner than in the cephalic half, and 

 extends in the direction of the tail, implicating one ring after another more 

 rapidly, until the whole is involved in decay*. 



If the Annelid were really endowed with the reproductive properties, which 

 by the most recent and distinguished naturalists they are reputed to possess, 

 such marvellous powers would undeniably have been called into activity by 

 the artificial division of the body. 



From the analogy of the two species, viz. Arenicola and Nais, on which 

 the author's observations have been chiefly conducted, the conclusion may 

 be deduced that the "fission of the body" in every other species of Annelida 

 in which it occurs, has for object in like manner to protect and incubate the 



* I have a distinct remembrance that many years ago, whilst studying physiology under 

 the zealous teachership of Mr. Grainger, experiments were related by that distinguished 

 physiologist, and oonducted by himself, with a view to resolve the enigma of the " myste- 

 rious tales" popularly prevalent with reference to the reproductive powers of the worms, 

 from which he drew conclusions precisely the same as those expressed iu the text. I can 

 now add ray testimony to the correctness of the observations, instituted for a diflferent pur- 

 pose, and so long ago, by one who has contributed not a little to the advance of physiological 

 science. 



