PLATE 6 



EXPLANATION OF FIfa'RKS 



26 Cienolahnis adspersus 9 X Fundula.'i hcterocl.ituts c^. Section through a 

 blastoderm which was killed fifteen hours and forty-five minutes after fertiliza- 

 tion. X 170. 



27 Cteriolabriis ads})ersus 9 X Ctenolaljrus adspemu.'i d' . Section through a 

 blastoderm killed thirteen hours and forty minutes after fertilization. X 170. 



28 to 33 Ctowlabrus adspersus 9 X Fundulus heteroclitus o" . 



28 A metaphase spindle of the second cleavage cut in three sections, showing 

 a mixture of short and long rods. 



29 An anaphase of the second cleavage in two sections. The long rods char- 

 acteristic of Fundulus and the shorter rods and hooks of Ctenolabrus are clearly 

 distinguished. 



30 Two sections of another spindle of the second cleavage. One section 

 shows only the longer chromosomes contributed by the sperm. The right- 

 hand section shows chromosomes of both parental tyj:es. 



31 Polar views of the two anaphase plates of one spindle. Second cleavage. 

 Forty-two chromosomes in each group. 



32 Anaphase of the fourth cleavage in four sections. An attempt was made 

 to draw all of the chromosomes. Only thirty-eight elements could be distin- 

 guished at either pole. 



33 One section of an ana])hase of the fourth cleavage. The three types of 

 chromosomes characteristic of Ctenolabrus, rods, liooks, and a V are shown as 

 well as the larger rods contributed by the spermatozoon of Fundulus. 



274 



