( 98 ) 

 PKOGKESS OF MICEOSCOPICAL SCIENCE. 



The Retrograde Development of Marine Bryozoa. — In the first number 

 of vol. xxi. of Siebold u. Kolliker's ' Zeitsclirift,' Claparede, wlio with 

 the exception of Nitzsche is the only writer who has studied the Bry- 

 ozfia since the publication of the capital papers of Smitt, gives us most 

 interesting contributions to their history. While on the main points 

 he completely agrees with the views taken by Smitt of the polymor- 

 phism of the species, their mode of budding and general embryonic 

 development, yet in some points not satisfactorily determined by Smitt, 

 such as the relations of the various cells (zooecia) to one another, the 

 nature of Smitt's " morka kroppar," dark bodies, and " fett kroppar," 

 he has new observations differing somewhat from those of Smitt. The 

 most interesting facts (which are recorded in ' Silliman's American 

 Journal,' by a writer who signs himself L. L. G., and who is perhaps 

 Agassiz) are those concerning a sort of retrograde development, a re- 

 sorption of the digestive cavity in the older cells, the gradual disap- 

 pearance of the lophophore, resulting in cells usually considered as 

 dead but in reality having lateut life, and where alone the fatty bodies 

 of Smitt, which play such an important part in the embryology of 

 Bryozoa, are developed. These cells apparently pass through stages 

 identical with those produced by budding at the youngest extremity 

 of the colony, with the difference that in one case the cell is immature, 

 while in the other it is fully developed. The resorption is frequently 

 accompanied by peculiar changes in these cells, and is confined to the 

 older portions of the Bryozoan colony in which the lateral connection 

 between the cells for exchange of fluids between the cells provided 

 with digestive cavities and those cells containing latent life, is very 

 strikingly shown, thus forming a complete circulation between the 

 most distant parts of the colony. He also confirms the nature of the 

 colonial nervous system, first traced by Fritz Miiller, and shows its 

 existence among the Chilostomata, where it had only been traced by 

 Smitt before. Claparede closes this interesting paper by giving us the 

 complete develoi^ment of Bugula, with larger, more accurate, and at 

 the same time more intelligible figures than we have had of the early 

 development of any one sjiecies of marine Bryozoa thus far. He has, 

 however, not been able to decide positively the nature of the ova, said 

 in one case to owe their origin to a sexual process, and in the other 

 cases to point to the existence of parthenogenesis among Bryozoa, imder 

 certain circumstances. Claparede has not confirmed the observations 

 of Schneider on the development of Membranipora, but from what 

 Nitzsche has observed of the early stages of Bugula, he appears to 

 have seen the same retrograde development in the youngest stages of 

 its larva which Schneider observed in Cyphonantes during its develop- 

 ment into Membranipora. 



The Coccoliths are Plants according to the recent inquiry of Mr. 

 H. J. Carter, F.R.S. They are what Professor Huxley first thought 

 them to be, not what he subsequently supposed in connection with his 



