22 Papers from the Marine Biological Laboratory at Tortugas. 



tigations with which I am acquainted it has been reported that the longi- 

 tudinal cleavage is first to be made evident in the prophase " believes that 

 " it is only logical to conclude that this division is completed by the first 

 spermatocyte mitosis." Upon the question of the sequence of the two sper- 

 matocyte divisions in Arthropoda the various workers are about equally 

 divided. McClung, in the case of some Orthoptera studied, believes that 

 the equation division comes first. Von Rath (1895), Henking (1890), 

 Paulmier (1899), and Montgomery (1898, 1900, and 1901) arrived at the 

 opposite conclusion in the case of various arthropods. Since the same 

 result is obtained for the spermatozoa in either event, this point is really 

 not of the vital importance it was formerly believed to possess. Neverthe- 

 less, it will be noted that during the later prophase, when the longitudinal 

 and transverse splits again close up and compact chromosomes are formed, 

 the long axis of these chromosomes does not appear to become the short 

 axis and vice versa, but the earlier proportions and relations are approxi- 

 mately adhered to ; therefore, since the first maturation division takes place 

 transversely to the long axis of the chromosome, it appears that the first 

 division of this mitosis is along the line of the second split marked out in 

 the early prophases. If the generally accepted interpretation of synapsis 

 is correct, i. c., that it represents an end-to-end (telosynapsis) union of two 

 chromosomes (paternal and maternal, Montgomery, 1901), and, further- 

 more, if these chromosomes do indeed separate during maturation along the 

 line of their previous fusion, then the tetrad figures of the early prophase 

 represent bivalent chromosomes divided first longitudinally or in the plane 

 of the long axis (fig. 67), followed by a transverse split, i. e.. along the 

 line of previous fusion and perpendicular to the long axis. Accordingly, 

 the first division of the long chromosomes at metaphase must represent the 

 transverse or second split of the early prophase and is a reducing division, 

 since it separates w r hole chromosomes. Figure 119 shows several of the 

 characteristic dividing figures (tetrads) of metakinesis. In the light of 

 these figures and the probable relations of the splits here shown to those 

 of the earlier prophase chromosomes, I believe that the first maturation 

 division is transverse and reductional and the second is longitudinal and 

 equational (including also the accessory). De Sinety interprets both divi- 

 sions as longitudinal in Lcptinia and Mencxenns. Due to the persistence 

 of connecting linin threads, Stevens (1905) was able to demonstrate very 

 conclusively that in Stenopelmatus (California sand-cricket) the first divi- 

 sion is longitudinal and equational. 



The chromosomes vary considerably in size and shape. Figure 80 shows 

 a typical spindle with variously shaped chromosomes. Spindles at meta- 

 phase invariably sho\v two pairs of reversed T-shaped chromosomes, three 

 pairs of long rod-shaped chromosomes, and the remainder are of the short 

 rod or dumb-bell-shaped types. Correspondences of size between the biva- 



