A Cytological Study of the Semi-iDarasitic Copepod, Hersilia apodiformis etc. 433 



In the Harpacticoida, in spite of the numeroiis marine and fresh- 

 water species (Sars '11), few forms have been studi^d cytologically, so 

 that it is impossible to State the main characteristics of this group. The 

 average chromosome number of the known fornis is ten, whereas that of 

 the preceding group is sixteen. The size differences are niore marked 

 than in the Calanoida, and the double rod (characteristic also of Group III) 

 supplants the ring-form tetrad of Group I. A study of the marine Harpac- 

 tids would doubtlessly give a much better idea of this group, for the 

 only fresh-water species so far studied nmst be looked upon as a highly 

 specialized species. 



III. Cyclopoida. 



Cydops strenuus . . 

 » insignis . . 



» dybowskii . 



» bicuspidatus 



» fuscus . . . 



)■- albidus. . . 



» leuckarli . . 



» serrulaius . 



11 of eqiial size, double rods with Querkerbe. B., M. 

 11 as in strenuus. B., M. 

 9 of equal size. B., M. 



size differences more marked than in previous 



species — 4 large, 5 smaller. B., M., Ch. 

 7 of equal size. B., M. 

 7 of equal size. B., M. 

 7 of equal size. B., M. 



(6 large and 1 pair of small hetero-chromosomes 

 < < which do not divide in 2nd matiu-ation divi- 



sion). B., M. 



(6 + 1 impaired small hetero-chromosome show- 

 phaleraius . . • J l ing "Querkerbe'' — divides oidy in 2nd matura- 



tion di Vision). B., M. 



of equal size. B., M. 



Ch. 



(1 large, 1 medium, 1 small) . Ch. 

 Ch. 



of equal size. B. 



5 + 1 small unpaired hetero-chromosome without 

 "Quer kerbe". B., M. 



5 + 1 unpaired hetero-chromosome of medium 

 size. B. Sometimes individuals show 6 + 1 un- 

 paired hetero-cLromosome. M. 

 or 5 + 1 small hetero-chromosome was present 

 in about 1/2 the individuals studied. M. 

 of equal size. B., M. 



11 + 1 smaller pair without "Querkerbe". K. 

 1 large, 9 medium. Much smaller than in Hersilia. 

 No "Querkerbe" could be seen in the oöcytes. K. 



28* 



Lidiomolgus forjicula . . 10 • 



