ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 193 



from one another by a ciliated groove, and this, too, is found in Anne- 

 lids ; it is this ciliated groove which by the growth and increase of its 

 elements forms most, if not all, of the ciliated epithelium of the 

 permanent central canal. 



Other points which favour the annelidan affinities of the Vertebrates 

 are the formation of the notochord and swimming bladder, the lateral 

 sense-organs, the characters of the nephridial system, and the agreement 

 between the development of the hypophysis cerebri of Vertebrates and the 

 development of the permanent oesophagus and its special nervous system 

 in Annelids. 



The Modern Cell-Theory.*— Prof. J. G. M'Kendrick traces the de- 

 velopment of the modern cell-theory through a long series of classical 

 investigations. The constitution and role of the nucleus and the phe- 

 nomena of division are discussed, while notice is taken of recent progress 

 concerning oogenesis, spermatogenesis, and fertilization. The bearing of 

 recent researches on the problems of heredity is then emphasized, and 

 several formidable objections are urged against Weismann's position 

 relative to acquired characters. 



B. INVERTEBRATA. 



Transversely Striated Muscular Fibre.t — Prof. A. Kolliker, in view 

 of the, as he thinks, erroneous teaching lately promulgated by A. v. 

 Gehuchten and Eamon y Cajal, gives an account of his own long con- 

 tinued observations on the structure of transversely striated muscular 

 fibre. The chief object of his investigations have been the fibrillar 

 wing-muscles of Insects : these are not found in all flying insects ; they 

 all consist essentially of two constituents, muscular fibrils and an inter- 

 mediate substance — sarcoplasm ; the fibrils are from 1-4 /jl broad, are 

 contractile along their whole length, and in a state of contraction, all 

 the parts are doubly refractive. When the fibres are at work there is an 

 active chemical action, and the rapidity of contraction in insects' fibres 

 may be ascribed to the large supply of tracheae. The chief seat of this 

 activity is the sarcoplasm, as the large quantity present and the fat- 

 molecules which are found in it are sufficient to show ; it is not to be 

 supposed, however, that the substance of the fibrils is not also ener- 

 getically changed. There is no coagulation of an albuminoid body 

 during contraction. If these views are correct it may further be 

 supposed that the fibrils consist of typically formed particles (the dis- 

 diaklasts of Briicke), the arrangement of which is the cause of isotropy 

 or of anisotropy, and which, during contraction, undergo changes of 

 position and form, the causes of which are to be found in electrical or as 

 yet unknown chemical processes. 



Number of Polar Bodies.! — Prof. A. Weismann replies at length to 

 an attack made upon him by Prof. Blochmann, in reference to the dis- 

 covery of the fact that only one polar body is formed in parthenogenetic 

 ova. The question is one both of priority and of accuracy of statement, 

 in regard to both of which Weismann more than vindicates himself. 



* Proc. Phil. Soc. Glasgow, xix. (1888) pp. 71-125. 



+ Zeitsohr. f. AViss. Zool., xlvii. (1888) pp. G89-710 (2 pis,). 



X Morpliol. Jahrb., siv. (1888) pp. 490-506. 



