A Cytolügical Study of the Semi-parasitic Copepod, Hersilia apodiformis etc. 431 



SYStematization." In his paper on the development QiAchtheres(WiLSO's, 

 Chas. B. 'IIa), he gives a table for the various groups of parasitic cope- 

 pods, showing the comparative time in development spent in the egg, 

 as free-swimmers, and as parasites. 



The ontogenetic study, especially of those forms which are pelagic 

 during the larval stages, involves great difficulties. It is perhaps not 

 unreasonable to inquire whether or not the cytologist can aid the em- 

 bryologist and systematist in a Solution of the problems presented. Will 

 a comparative study of the chromosomes show such distinetive forms 

 in the various larger groups of the Copepoda, as a study of the Inseeta 

 has done? For example, could a cytological study decide whether the 

 degenerate Chondrocanthidae belong in the third group, the Cyclopoida 

 (Sars' Classification, footnote on p. 429), with the Corycaeidae and Erga- 

 silidae; or in the seventh group, the Lernaeoida. degenerate tish parasites 

 which the Chondrocanthidae resemble in their adult form? 



A definite answer to this question can not at present be given, for, 

 of the seven sub-orders of the Copepods, only three have been studied 

 to any extent, and these only in a few genera. The first sub-order, the 

 Calanoida, has been most broadly studied and here there are similarities 

 to be found which are characteristic throughout this group. In the 

 Copepod egg, the average number of chromosomes, the form taken by 

 them in the germinäl vesicle at the end of the growth period, and the 

 form in the first maturation spindle will, I believe, off er a basis for com- 

 parison; and it is just these facts which are usually obtainable, the stages 

 being of long duration. The structure of the gonads, the form of the 

 "Keimpolster", the size of the germ cells, their spindle and nucleoli may 

 be studied at the same time and aid in comparison. The possibility of 

 such a comparative study presented itself to the author while examining 

 the sexual elements of the most common free-swimming and semi-para- 

 sitic Copepods of the Bay at Naples. The chromosomal differences were 

 most striking. The work is at present only a begirming, but it is hoped 

 that in the future a more extended and systematic account with size 

 measurements of the chromosomes and germ cells may be published. 

 The foUowing is a tabulation of the present data on the Copepods, but 

 this data is still too incomplete to Warrant definite conclusions ; however, 

 judging frora the Calanoida, it would seem that a broader study of the 

 other groups, including their most characteristic f amilies, would not 

 be without results. 



In the tables the Classification of Sars (Footnote 1, p. 429) will be 

 adhered to, and whenever possible the number of chromosomes in the 



Archiv f. Zellforschnng. XIII. 28 



