24 LECTURE II. 



stages of the development of the germ, as figured by Siebold in the 

 Strongylus and Medusa, by Baer in the frog, and by Barry in the 

 rabbit. Dr. Martin Barry, who has discovered the very remarkable 

 and complicated nature of this process in the mammalian ovum, was 

 alone perhaps in the condition to fully comprehend and explain its 

 analogy to the fissiparous generation of the Polygastria, to which, 

 in 1840, I briefly alluded; and this he has done in a paper, replete 

 with interesting generalisations, lately read before the Royal Society. 

 I have been favoured by that indefatigable observer with the following 

 notes of his ideas on this subject. 



" Between the appearance presented by the mammiferous germ 

 during the passage of the ovum through the Fallopian tube, and those 

 met with in the young Volvox globator while within the parent, I find 

 a resemblance which is very remarkable indeed, extending even to 

 minute details. Not only do the cells of which the young Volvox is 

 composed form a body resembling a mulberry, with a pellucid centre, 

 but the cells gradually increase in number, apparently by doubling, 

 at the same time diminishing in size, like the cells of the mammi- 

 ferous germ ; which they resemble also in being originally elliptical 

 and flat. 



" Some of the points of resemblance now mentioned were recog- 

 nised in the delineations of the Volvox given by Professor Ehrenberg ; 

 others were noticed during some observations I have myself made on 

 this very interesting microscopic object. Professor Ehrenberg has 

 figured five pellucid globules in a young Volvox just escaped from the 

 parent. These, the germs of another set, evidently resulted from di- 

 vision of the pellucid mass visible in an earlier state : so that here is 

 to be recognised fissiparous generation of the kind I have described 

 as reproducing cells. 



" On examining the figures given by Ehrenberg of successive genera- 

 tions of the Chlamydomonas (^"^. 

 14.), I see a resemblance to the 

 two, four, eight, &c. groups of 

 cells in the mammiferous ovum 

 too striking, not to suggest that 

 the process of formation must be 



ChlamyJoinonas. "^ 



the same in both : the essential 

 part of this process consisting in division of the pellucid nucleus. 

 And it is deserving of remark, that Ehrenberg describes his Monas 

 hicolor, evidently a nucleated cell, as possibly an early state of the 

 Chlamydomonas. 



" The curiously symmetrical forms of many of the JBacillaria appear 

 to be due to this two, four, eight, &c. division of the nuclei of cells. 



" The delineations of Gonium, Manas vivipara, and Ophryditmi 



