DESCRIPTIONS OF GENERA AND SPECIES 657 



glandular appearance, red in colour and without setae, suggesting that it was the 

 point at which new segments were formed. PERRIEK, in his account of the anatomy 

 of this species, saw the same swelling upon the body, which was, in his specimens, 

 nearly constant; he found that its commencement coincided with the termination of 

 the typhlosole. I myself examined the same region by means of sections, and 

 confirmed the idea of Mt)LLER ; I found, however, that the setae are not universally 

 absent, but that they are rare, and, when present, are of small size, suggesting 

 embryonic setae ; the epidermis too is without the glandular cells found elsewhere, 

 another character suggesting an embryonic condition ; the intestine lying in these 

 three or four segments was narrower than elsewhere, and was found to be devoid 

 of contents. This interesting subject has been recently more fully dealt with by 

 HORST (17). In addition to confirming the facts described by his predecessors, the 

 caudal zone was stated to be remarkable on account of the large development of 

 blood-vessels. HORST has justly pointed out that there is, after all, not much in 

 favour of regarding this tract as a zone of growth, which, indeed, as PEERIER said, 

 would be, if it existed, an entirely exceptional state of affairs. The nephridia show 

 no signs of an embryonic state, nor do the septa or the nerve-chord. HORST, therefore, 

 while unable to offer any suggestion of his own, declines to accept the view of MULLER 

 and myself. I am now inclined to adopt a modification of those views ; it seems to 

 me possible that this region of the body is still a zone of growth, as any part of 

 the body is when by an accident it becomes the end of the body ; the tail of a worm 

 will, as we know, regenerate when it has been torn off; it is quite common to meet 

 with worms with the end of the body of much less calibre than the rest, which 

 shows that this part has been recently renewed after an accident. The rich blood- 

 supply, and the, to some extent, embryonic character of the epidermis in the caudal 

 zone, would possibly favour rapid regeneration ; while the swollen character of this 

 part of the body might very easily bring it about that the tail-end of the body, the 

 part lying behind it, would be readily detached ; perhaps it would more probably be 

 broken in the middle ; in this event, the regeneration would, ex hypothesi, be more 

 rapid than if the body were broken elsewhere. On this view the structure in 

 question is analogous to the foot of certain Mollusca, to the structure of the 

 backbone in certain reptiles, which readily break at a certain point, allowing 

 the animal to escape. It seems, however, that the mechanism is rather more 

 perfect in the worm than in the other animals ; not only is breakage facilitated, 

 but there exists the power of a more rapid reconstruction of the injured part. This, 

 however, must obviously remain for the present no more than a suggestion. 



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