298 JAMES RANKIN, 



observations that the breaks in the muscle layers of the tail of 

 Appendicnlaria arc "purely accidentar\ but remarks that the occur- 

 rence of the "splits" at definite intervals may be influenced by the 

 rep;ular occurence of the paired nerves althoup;h he says that he has 

 been unable to stain satisfactorily "the nerve cord and 'spinal' nerves'\ 

 He is inclined to regard the breaks in the muscle bands as being 

 "the first step towards an incipient vertcbration". Lkfevke does not 

 give the genera or species of the animals on which his observations 

 were made. 



In the other paper Seelioer ' ) states that having received fresh 

 material he has been enabled to complete his former observations. 

 He says "Die vermeintlichen 'Segmentgrenzen', die bei geeigneter Be- 

 handlung auftreten, sind also lediglich die Grenzen zwischen je zwei 

 Muskelzellen und unterbrechen nicht einmal die Continuität des 

 Fibrillenverlaufes. Erst nach langer Einwirkung bestimmter Reagentien, 

 oder wenn beim Tode des Thieres eine Auflösung der Muskelbänder 

 in die einzelnen Zellen erfolgt, reissen die Fibrillen an diesen Stellen 

 entzwei. Die Muskelzellen der rechten und linken Seite liegen ein- 

 ander ziemlich genau gegenüber". The animals examined were F. fur- 

 cata and 0. cophocerca. 



I do not know from what evidence Seeliger reaches these con- 

 clusions, but I find myself quite unable to accept them. A further 

 examination of my preparations tends to confirm the statements 

 already made. 



1) There appear to be two rows of cells concerned in the form- 

 ation of the middle and anterior parts of the muscle band of each side. 

 Reference has already been made to the bilateral api)earance of the 

 reticulations in F. furcata and 0. dioica. In some of my preparations 

 of the former species the reticulations of the anterior two thirds of 

 the tail are almost completely divided in two, the halves being con- 

 nected by a very few slender nuclear threads. None of my pre- 

 parations of F. furcata show a series of muscle "segments", but, judging 

 from their appearance in O. dioica, when they do occur the "segments'" 

 of each side i)robabIy correspond to each other more or less exactly. 

 But the nuclear reticulations certainly do so only in very few in- 

 stances. More especially the nuclear structures which are situated 

 between the posterior pair of large gland cells vary in jtosition niar- 



1) 0. Rkri,i(;kr, Die Bedeutung der „Sédimentation" des Ruder- 

 schwanzea der Appendicularien, in: Zool. Anzeiger, No. 446, 1894. 



