Maech 27, 1903.] 



SCIENCE. 



485 



A. The free-living copepods, Gnathosto- 

 mata. 



B. The parasitic copepods, Siphonosto- 

 mata. 



C. The Branchiura or Argulidse, also 

 parasitic. 



The normal development of the cope^ 

 pods, viz., of the Gnathostoniata, is well 

 known to every teacher of zoology, and all 

 have become familiar with the nauplius, 

 metanauplius and cyclops stages in their 

 life history. But the development of the 

 Siphonostomata is still very imperfectly 

 known, and while agreeing in many species 

 with that of the free-living forms, there 

 are frequent modifications resulting from 

 parasitic habits. 



The development of the third group, the 

 Argulidee, has rested until recently upon 

 the study of a single European species, 

 A. foliaceus, parasitic upon fresh-water 

 fishes. 



But the Argulidse are found in greater 

 abundance in North and South America 

 and in Afi-ica than in Europe, and are 

 fairly well divided between fresh-water 

 and marine forms. 



A recent study of four American species 

 shows that two of them, A. americanus and 

 A. catostomi, the former a fresh-water spe- 

 cies and the latter occurring in both fresh 

 and brackish water, agree almost exactly 

 with A. foliaceus in development. 



But the life history of the other two 

 species, one, A. stizostethii, a fresh-water 

 form, and the other, A. megalops, which is 

 marine, is quite different. In both these 

 species the newly hatched larva is almost 

 exactly like the adult. There is no narrow- 

 ing of the body posteriorly, the abdomen 

 being fully as wide as the thorax and of 

 the same shape as in the adult. 



The carapace is somewhat shortened, but 

 even when fully developed it is very 

 meager. The number and arrangement 



of the appendages are exactly the same as 

 they will always continue. 



The form and function of these append- 

 ages are also the same, with the single ex- 

 ception of the first maxillipeds, and even 

 here, while the form changes, the function 

 remains constant from the beginning. 

 There is no trace of a temporary locomotor 

 apparatus of any sort or description, as in 

 all other copepod larv^. We have here, 

 therefore, practically no metamorphosis at 

 all, but a copepod life history which is 

 virtually a direct development, and there 

 is a marked resemblance to the life history 

 of certain orders amongst the insects, such 

 as the Orthoptera, etc. 



The Arrangement of the Segmental Mus- 

 cles in the Geophilidw, and its Bearing 

 upon the Double Nature of the Segment 

 in the Eexapoda and Chilopoda: L. B. 

 "Walton, Kenyon College. 

 The arrangement of the dorsal lateral 

 longitudinal muscles in the GeophilidaB 

 corresponds to the division of the segment 

 into an anterior and posterior somite. 

 This, considered in connection with the 

 presence of homologous areas in Scolopen- 

 drella, Campodea, Japyx, Forficula, etc., 

 together with other evidence, notably the 

 development of the pterygodum (tegula) 

 and wing of the mesothorax in Lepidoptera, 

 the double cross commissures in the em- 

 bryonic stages of Hexapoda and Chilopoda 

 (as well as Crustacea and Araehnida), 

 the two pairs of metathoracic tracheal 

 openings in Japyx, etc., presents a strong 

 case for regarding the segment in the 

 Hejfapoda and Chilopoda as composed of 

 two somites, for which the terms proto- 

 somite and deutosomite are proposed. 



The 'mierothorax' to which Verioeff has 

 recently called attention as a fourth tho- 

 racic segment anterior to the prothorax 

 (Dermaptera) can not be homologized, as 

 he suggests, with the segment bearing the 



