426 Sidney I. Kornhaiiser 



lished figures of their results ou Euchaeta nonvegica^), in whicli tliey 

 found a parallel conjugation. They claim (Schreiner's '06b), froni th-eir 

 own experience, that the material is a difficult one, and that it is not 

 surprising to find that, in the earlier investigations of Haecker, vom 

 Rath and Rückert, the conjugation of the chromosomes was over- 

 looked. They state further that the older observations can not be used as 

 an argunient against theu* results and those of Lerat on Cydops sirenuus. 

 McClendon ('10) has shown that a parallel conjugation of the chromosomes 

 exists also in the parasitic Copepod, Panäarus. Thus, in four widely 

 separated types: (1) EucJiaeta nonvegica, a marine Calanid; (2) Cyclops 

 stremms, a fresh-water Cyclopid; (3) HersiUa apodiformis. a semi-parasitic 

 Hersiliid; and (4) Panäarus sinuatus, a parasitic Caligid, — the process 

 of parasyndesis has been shown to take place. 



After these discoveries, we can scarcely speak longer of a "primary" 

 and "secondary" longitudinal division of the chromosomes of the first 

 maturation spindle. The "primary" longitudinal division is rather the 

 plane of conjugation of two chromosomes; and, in the spermatogenesis 

 of HersiUa, it has been shown that the chromosomes come apart along 

 this plane and usually straighten out into long rods, which remain 

 connected at one end and stand vertically in the spindle (Fig. 29, 

 Plate VI). The "secondary" longitudinal division is the real and only 

 longitudinal division of the chromosomes, and is the plane of Separation 

 of the chromosomes in the second maturation division (Figs. 35, 36, 

 Plate VI). HersiUa is in complete agreement with the classical work 

 of the Schreiners on Tomopteris, and a clear case of the hetero- 

 homeotypic method of maturation. 



C. Chromosomes and Phylogenetic Relationship. 



The question whether the chromosomes can be used as an index 

 to the phylogenetic standing of closely related species or genera has been 

 most admirably and instructively discussed during the past year by 

 Federley ('13). Likewise Miss Browne ('13) has reviewed the subject 

 very thoroughly in a consideration of the possible homologies between 



1) The marine Calanids, as Euchaeta and Calanus, and the fresh-water Cyclopidae, 

 according to ijersonal investigation, are the niost difficult of Copepod material. The 

 former have in the reduced number no less than sixteen or seventeen chromosomes, 

 and in the latter almost invariably come large shrinkage spaces, as shown in Lerat's 

 figures. Thus, it would seem that either the smaU males of semi-parasitic or parasitic 

 species, with thin cuticula, or the males of large parasitic species fi-om which the sex 

 glands coiüd be dissected before fixation, such as Panäarus or Ceeropes, would offer 

 far better material. 



