266 LECTURE Xllf. 



LECTURE XIII. 



EPIZOA AND CIRRIPEDIA. 



The phenomena of the generation and development of the animal 

 kingdom, so far as we have traced tliem, must, ah-eady, have impressed 

 us with the inadequacy of the linowledge of tlie nature of an animal 

 in its final and complete stage of existence only, for the determination 

 of its affinities and proper place in the natural system. This we have 

 learnt from a study of most of the previous classes of animals ; it is 

 more plainly demonstrated by the subjects of this day's discourse. I 

 may also here observe, that whilst it is essential to trace the meta- 

 morphoses of each species in order to rightly comprehend its true 

 nature, the study of the generative organs shows that we cannot rely 

 on them alone for a system of classification. We saw, for example, 

 that some of the anellids combined both male and female organs in 

 the same individual, while others had those organs separate and 

 peculiar to distinct individuals ; one order was androgynous, another 

 dioecious. In the earth-worm we had evidence of a certain concen- 

 tration of the generative system within a few segments; in the leech, 

 of a sub-division and more extended placing of the male organs : 

 but this vegetative character was most remarkable in the dioecious 

 anellids, in which almost every joint presented either its pair of testes 

 or of ovaria, according to the sex of the individual. Then, in refer- 

 ence to the progress of development of these worms, some transitorily 

 manifested the form and character of one class, inferior to them in the 

 animal scale, and others those of another lower class : thus the 

 embryo leech represents the planaria, whilst most of the higher 

 anellids quit the ovum in the infusorial form. The further progress, 

 of development was interesting, since it reminded us of that singular 

 propagation of certain Acalepha;, in which the larva produced other 

 larva3 like itself, before it was metamorphosed into the final form of a 

 medusa. For the ordinary mode of growth of the Anellid, by the 

 development of joint after joint, one precisely similar to the other, 

 throughout a series of, perhaps, hundreds of joints, with only the first 

 and the last segments distinguished by any peculiar characteristics, — 

 all this process of growth looked very like an incomplete partheno- 

 genesis ; but this mode of production is fully manifested by the suc- 

 cessive casting oiF of groups of segments, with the characteristic head 

 and tail, as in tlie instances cited in the preceding Lecture ; the young 

 anellid from the ovum propagating at first by gemmation and spon- 



