A Cytological Study of the Semi-parasitic Copepod, Hersilia apodiformis etc. 42 9 



the insects are classed. The large cells and long curved chromosomes 

 of Orthopterans ; the shorter, thick, clear cut chromosomes of the Hemi- 

 ptera; the sniall spherical chromosomes of the Lepidoptera; and the 

 numeroiis minute chromosomes of the Hymenoptera: each is character- 

 istic for its order. Should a cytologist, well acquainted with the sperniato- 

 cytes of the various Orders of insects, receive for examination a species, 

 which through parasitism had lost the morphological (somatic) characters 

 of the order to which it belonged, could he determinc in which order it 

 should be placed from an investigation of the spermatocytes? Were the 

 niembers of this order well known cytologically, the question would prob- 

 ably be answered in the affirmative. 



Problems of this nature are far niore nunierous in a consideration 

 of the Copepods, the majority of which are either parasitic or semi-para- 

 sitic and the systematic relationship of the families to one another and 

 to the free-swimming forms is often but a matter of conjecture. 



D. The Classifleation of the Copepods. 



The Copepods must be looked upon as a highly successful group of 

 organisms, plastic and capable of living under the most diverse conditions: 

 as free-swimmers in salt and fresh water, as commensals or semi-parasites, 

 or as total ecto- or ento-parasites. In the phylogenetic history of this 

 group, parasitism has certainly been entered upon more than once, so 

 that the various Copepod parasites belong to widely separated sub-divi- 

 sions of this order. Even in the Harpacticoida, which to the present 

 time have been known only as free-swimmers, a parasitic species, Uving 

 on the gills of the common land crab of Jamaica, has been described 

 by Professor Chakles Wilson ('13). This investigator has discussed 

 the Classification of the Copepoda in a most instructive manner (Wilson, 

 Chas. B., '10). In accepting the Classification of Sars ('10)^), h :• points 

 out the weaknesses of all the previous methods of sub-dividing this order; 

 and shows that, while the first antennae are the most conservative organs, 

 yet neither they, nor the mouthparts, nor the body form, all of which 



1) From Chas. B. Wilson ('10, p. 619), "We have the order Copepoda sub-divided 

 into seven sub-orders: "1. The Calanoida, free-living and pelagic; 2. the Harpacticoida, 

 also free-living but demersal ; 3. the Cyclopoida, partly free-Uving and fresh-water spe- 

 cies, partly commensals and messmates with other animals, partly parasitic; 4. the 

 Notodelphyoida, semi-parasitic and living upon ascidians and similar animals; 5. the 

 Monsirilloida, partly parasitic and partly free; 6. the Caligoida, parasitic upon fishcs, 

 moderately degenerate.and with some freedom of motion; 7. the Lernaeoida, fish para- 

 sites, strongly degenerate, fixed in position, and with marked sexual dimorpliism.'- 



