44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



Any work in connection with the head of an invertebrate such as 

 Peripatiis inevitably must include a discussion of segmentation. Of 

 the many workers who have applied themselves to this problem there 

 are several who in late years have either contributed original data as 

 a result of their own research or have written compilations that are 

 extremely valuable to the anatomist. Of these workers, Federov 

 (1929) alone of the group confined himself to a single organ system 

 of the adult in his two extensive papers on the nervous system of 

 Peripatiis tholloni. Realizing the importance of the nervous system 

 as a criterion of segmentation, he tried to identify segmental areas 

 in the ventral nerve chain of the animal and to correlate the cerebral 

 nerves with the nerves of these segmental areas. 



Pflugfelder (1948) in a paper on the embryology of Paraperipatus 

 amboinensis comes to conclusions concerning head segmentation that 

 support Federov's ideas. Pflugfelder, however, was handicapped by 

 the fact that he apparently considered the jaws of Peripatus to cor- 

 respond to the mandibles of the arthropods, and he formulated his 

 arguments to prove this point, a fact which I think limits the value 

 of his work. 



Manton in a series of papers published after 1938 has given very 

 valuable accounts of the embryology, anatomy, and habits of Peri- 

 patus. But her work on embryology was mainly concerned with the 

 thesis that segmentation is instigated by the mesoderm and that in this 

 respect the nervous system is of little importance. More will be said 

 about the work of these two later in this paper, 



Snodgrass, in his paper of 1938 on the Annelida, Onychophora, and 

 Arthropoda, gave a remarkably clear and complete description of the 

 development and anatomy of this animal. 



Weber, in his "Morphologic, Histologic und Entwicklungsgeschichte 

 der Articulaten" published in 1952, devoted a lengthy section to the 

 Onychophora in which he compared the ideas of L. M. Henry (1948) 

 to those of Pflugfelder published the same year. He agrees with 

 Pflugfelder's opinion that the jaws of the Onychophora are the true 

 mandibles as opposed to Henry's statement that they belong to the 

 tritocerebral segment. In his paper Weber quotes Pflugfelder at length 

 in regard to principles to be followed in homologizing organs in dif- 

 ferent groups of animals. He says, "Care must be taken not to ho- 

 mologize in all details the tritocerebrum of the Onychophora and the 

 stomatogastric nerves emanating therefrom with the tritocerebrum of 

 the Arthropoda on the one hand and the corresponding parts of the 

 nervous system of Annelida on the other. The Onychophora do not 



