132 



ANATOMY AND PHYSIOLOGY OF 



bear an inverse ratio to the degree of devel- 

 opment which has previously taken place 

 in each case. Thus, in the Hydra and 

 other Zoophytes, it would appear (as in 

 Plants) to be almost unlimited ; for the de- 

 velopment process in them is checked at 

 such an early period, that both the form of 

 the organism and the structure of its tissues 

 retain the most simple type ; and by the 

 subdivision of one individual, no fewer 

 than fifty were produced by Trembly. In 

 this, as probably in all the cases in which 

 new indi\iduals have been obtained by 

 artificial subdivision, there is some natural 

 tendency to their production by the vege- 

 tative process of gemmation ; but tliis does 

 not always manifest itself. It is a curious 

 fact, that the first attempt at regeneration, 

 in some of these cases, is not always com- 

 plete ; but that successive efforts are made, 

 each of which approximates more and 

 more closely to the perfect type. This was 

 well seen in one of Sir J. G. Dalyell's ex- 

 periments; for he observed that, having 

 cloven the stem of a Tubularia (a Hydroid 

 Zoophyte), after the natural fall of its head, 

 an imperfect head was at first produced, 

 which soon fell off and was succeeded by 

 another more fully formed ; this in its turn 

 was succeeded by another ; and so on, until 

 the fifth head was produced, which was as 

 complete as the original. 



" As a general statement of the amount 

 of this regenerating power, which exists in 

 most of the different classes of animals, 

 has been already given, it is unnecessary 

 here to do more than allude to some of 

 those facts which most strongly bear out 

 the doctrine just laid down. Next to 

 Zoophytes, there are no animals in which 

 the regenerative power is known to be so 

 strong as it is in the lower Articulata (as 

 the Cestoid Entozoa, and the inferior An- 

 nelida), and in the Planaria, which may 

 perhaps be regarded as rather approximat- 

 ing to the Molluscous type ; and here, again, 

 we see that a low grade of general devel- 

 opment is favorable to its exercise, and that 

 the spontaneous multiplication which occa- 

 sionally takes place in these animals by 



fission or gemmation, is only another form 

 of the same process. In the higher forms 

 of both these sub-kingdoms, as we no 

 longer meet with multiplication by gemma- 

 tion, so do we find that the reparative power 

 is much more limited ; the only manifesta- 

 tion of it among the fully-formed Arrach- 

 nida and Crustacea being the reproduction 

 of limbs, and the power of effecting even 

 this being usually deficient in perfect In- 

 sects. The inquiries of Mx. Newport, 

 however, upon the reproductive powers of 

 Myriapods and Insects, in different stages 

 of their development,* confirm the general 

 principle already stated ; for he has ascer- 

 tained that in their larval condition, Insects 

 can usually reproduce limbs or antennae ; and 

 that Myriapods, whose highest development 

 scarcely carries them beyond the larvae of 

 perfect Insects, can regenerate limbs or an- 

 tennae, up to the time of their last moult, 

 when, their normal development being com- 

 pleted, their regenerative power seems en- 

 tirely expended. The Phasmidce and some 

 other insects of the order Orthoptera retain a 

 similar degree of this power in their perfect 

 state ; but these are remarkable for the similar- 

 ity of their larval and imago states, the latter 

 being attained, as in Arachnida, by a direct 

 course of development, without anything 

 that can be called a ' metamorphosis.' Lit- 

 tle is known of the regenerative power in 

 the higher Mollusca; but it has been 

 affirmed that the head of the Snail may 

 be reproduced after being cut off, provided 

 the cephalic ganglion be not injured, and 

 an adequate amount of heat be supphed. 

 In Vertebrata, again, it is observable that 

 the greatest reparative power is found 

 among Batrachian Reptiles, whose devel- 

 opment is altogether lower, and whose life 

 is altogether more vegetative, than that of 

 probably any other group in this sub-ldng- 

 dom. In Fishes, it has been found that 

 portions of the fins which have been lost 

 by disease or accident are the only parts 

 that are reproduced. But in the Sala- 

 mander, entire new legs, with perfect bones, 

 nerves, muscles, etc., are reproduced after 



* " Philoijophical Transactions," 1844. 



