A Cytological Study of the Semi-parasitic Copepod, Hcrsilia apodifnrmis etc. 403 



otherwise, the salts of the sea water formed precipitations on the chitin, 

 which interfered with a rapid penetration of the fixative. Flemming's 

 fhiid (strong) and Carnoy (chloroform, alcohol, glacial acetic acid without 

 subhmate) were the only fhiids which gave satisfactory results. The 

 former was allowed to act from ten to twenty minutes, the latter only 

 three to five minutes. The smallness and flatness of Hersilia and the 

 thinness of the intersegmental membranes permits a rapid penetration^) 

 of the fixing fluid. Those fixed in Flemming's fluid were washed in 

 runnino- or often distilled water for ten or twelve hours. To facilitate 

 handling, when males alone were imbedded, they were first enclosed, in 

 lots of fifty or more, in Cryptobranclms epidermis. Chloroform was used 

 as the medium previous to emljedding, and the animals were allowed 

 to remain in the thermostat only twenty minutes, and during that time 

 changed to fresh paraffin two or three times. All sections were cut 5 micra 

 in thickness. The egg sacks were embedded in celloidin paraffin (Apathy 

 '13) and also cut 5 micra. 



The principal stains used were Heidenhain's haematoxylin and 

 crystal-violet-alizarin, the latter being employed only on Flemming 

 material. Borax carmine and Delafield's hämatoxylin and safranin 

 were used also at times for a study of the cleavage chromosomes. 



IV. Structure of Testes and Ovaries. 

 A. Testes. 



The testes are paired organs {te. Figs. A—B), lying dorsal and 

 medium in the thorax. There is an unpaired "Keimpolster"^) (Plate IV, 



1) Non-penetration of fixiiig fluids can not entirely account for poor fixation 

 in the testes and ovaries (growth period) of many Copepods. After working for four 

 months on various fresh water Cyclopidae, using fixatives of all possible combinations 

 or warm fluids, cutting or piercing the animals before fixation, I was imable to secure 

 good preservation of spermatocytes or young oöcytes. Diaptomus coerukus, without 

 cutting or piercing the animals, aUows of good fixation in Herm.ann's fluid; but the 

 long dm-ation of the "confused stage" (Wilson, '13) makes it undesirable for a study 

 of s\Tidesis. 



At Xaples, many Calanids, including Änomaloccra, Euchaeta, Eucnlanus and 

 Calanus, were either slit open in the fixing fluids, or had the anterior and posterior 

 ends cut off in the fixing fluid with a fine scissors; but all in both sexes showed 

 the chromatin tightly knotted in the early growth period. Of the Ascidicolae Noto- 

 pterophorus, Nolodelphys and Lichomnhjus fixed well in Flemmimg, as did the male of 

 Sapphirina ; but in all these forms, the smallness of the germ cells and the minuteness 

 of the chromosomes make them less favorable than Hersilia for a study of syndesis. 



2) The "Keimpolster'- itself is separated from the testis proper by a membrane, 

 and even in young individuals the cells of the "Keimpolster" have almost no stainable 



