LECTURES ON EMBRYOLOGY. 



ta&fc free one, is still a point which only di- 

 rect investigation can ascertain. I incline to sup- 

 pose, that the Medusa-like germs which are devel- 

 oped from the bunches of eggs, hanging below the 

 outer tentacles, are the intermediate, free genera- 

 tion which grows to lay moveable eggs, similar to 

 those of Campanularia^ and that these eggs, and 

 not the soft free buds, grow into Tubularise. How- 

 over, so much, at least, can already be inferred 

 with precision: that Tubulari must have some 

 free generation, a generation which is about to 

 attach itself in tke latter part of September, and to 

 produce a luxuriant growth of common branching 

 Tubularise. 



Now, how rapid this growth must have been, and 

 how rapidly the branches must have succeeded, an 

 illustration of the details will show. Each single, 

 isolated stem, from five to seven inches long, ter- 

 minates with a crown, having its tentacles and 

 bunches of eggs, like the most perfect Tubularia I 

 have seen. The terminating Polyp has bunches of 

 eggs, and all these eggs have already their yolk, 

 with its envelope their germinative vesicle, with 

 its geriainative dot. The lateral branches, per- 

 Qaps five or six, in \ arious stems, growiag from 

 different parts of the stem {but the lower always, 

 in every case, being longer than the upper ones J 

 were terminated also with regular crowns ^ but 

 Chose smaller and simpler individuals, the number 

 of their tentacles being fewer, were found to be 

 without any eggs. They had not grown to the 

 formation, to the development of organs of repro- 

 duction. The tertiary branches, sometimes as 

 many as five or six upon one of tke secondary, 

 were found to terminate also with a small Polypi 

 but like the secondary, to be without eggs. Hun- 

 dreds of these branches, compared together, show- 

 ed no difference. They were so alike as to indi- 

 cate, distinctly, that they were the growth of one 

 epoch ; that they had been attached to the vessel 

 <at one time, and had grown under identical cir- 

 cumstances. That stems already formed, could 

 not be attached to tke vessel, is shown by the cir- 

 cumstance that the loose branches sink to the bot- 

 tom, and have no means of transportation from 

 one place to another, Thus, the being which was 

 fixed, must have been a free animal. You remem- 

 ber, perhaps, what I have said in a former lecture 

 upon the embryonic growth of Tubularise. I 

 showed the formation in the bunches of eggs of 

 little Medusa-like beings, with four or more arms, 

 four prominent ones, and others alternating with 

 shem, less developed, which became free, bat 

 whose nal development had not been observed, 

 I now suspect that these Medusa-like buds would 

 grow into Medusa-like animals, and that these 

 Medusa-like animals would lay eggs, and that 

 these eggs, like those of Campanula^, being first 

 free, would then become attached grow to a disk- 

 like surface, rise from the centre to a stem-like 

 growth, and then pass through the same meta- 

 morphose? whicb have been observed ia tae Cam- 



panularias. At all events, here is one fact it 

 history of this animal ascertained, which wa 

 known before the fact of its rapid growth, o. J1* 

 rapid branching, and of the existence of a free 

 generation, though not ascertained by investiga- 

 tion, so strongly indicated by circumstantial evi- 

 dence as to be almost a positive fact, in the opin- 

 ion of one who has been accustomed to compare 

 these phenomena and to refer them to a common 

 type. 



In my last lecture, the first upon articulated an- 

 imals, I began by illustrating, in a general man- 

 ner, the character of the great and numerous type 

 of Articulata^ how they are subdivided into three 

 classes the Worms, Insects and Crustacea or 

 in the order which I would prefer, Worms, Crus- 

 tacea and Insects ; then further, I alluded to the pe- 

 culiar characteristics of insects, to their extensive 

 metamorphoses ; and then more fully illustrated 

 the embryonic growth of these animals, as as- 

 certained by the investigations of Professor Kolli- 

 ker; and finally investigated the different meta- 

 morphoses in different families of Insects, 



We now proceed to the investigation of the 

 changes of structure which these insects undergo 

 during their metamorphoses. We have examined 

 the general changes of form which these animals 

 undergo in various families. We have now to ex- 

 am iae the changes in the internal structure, which 

 take place in the larvse of Insects, till they acquire 

 their perfect development. And in tracing these 

 changes, we shall acquire an invaluable key to ap- 

 preciate the relative value of the differences which 

 exist between all insects between articulated ani- 

 mals at large. 



If it is true that Insects are the feighest among 

 articulated animals, even if they should occupy a 

 second rank, a thorough acquaintance with all the 

 changes of structure which they undergo during 

 growth, must give us a key to appreciate the real 

 value of these differences, their relative order of 

 succession in a scale in a gradation of structural 

 differences, 



The value of these comparisons must be so ob- 

 vious, that I need not apologise for dwelling more 

 extensively upon these topics than I would other- 

 wise, i repeat it that the facts which we are 

 now about to examine will famish (if there is one) 

 the key for estimating the value of characters in 

 one of the greatest types of the animal kingdom. 



In Plate XII are diagrams representing the ner- 

 vous system of a White Butterfly. (which is exceed- 

 ingly common in Europe) living upon cabbage, 

 in its various stages of growth, as figured by 

 Herold,.in his remarkable work upon the metamor- 

 phoses of that animal. In Plate XIII are diagrams 

 representing the changes which take place in the 

 digestive apparatus of the same animal ; and here 

 <in Plate XIV, figs. A and B) are represented lon- 

 gitudinal sections of a Moth <Fig. A) and its Cater- 

 pillar form (Fig. B) from Prof. Newport's research- 

 es, to show the different systems of organs in their 



