262 H. J. VAN CLEAVE 



ordinarily be subordinated to those upon carefully prepared 

 serial sections if points of structure are to receive a final analysis. 

 Hamann ('91, p. 28) refers to the condition of the subcuticular 

 nuclei of Echinorhynchus clavaeceps, now Eorhynchus agilis, 

 in the following terms: 



Das Larvenstadium, in dem die Haut ein Syncytium mit wenigen 

 Riesenkernen bildet, ist bei Echinorhynchus clavaeceps dauernd fixiert. 

 Wie ich in dem systematischen Teil zeigen werde, ist diese Art auf dem 

 Larvenstadium stehen geblieben, was ihre Haut, Muskulatur, Lemnisken 

 anlangt, wir haben einen Fall von Phylo-Paedogenesis vor uns. 



Eereits am lebenden Thiere sieht man die 0.2 mm. grossen, eiformigen 

 bis kugeligen Riesenkerne in der Haut. Ich zahlte bei dem in Fig. 1 

 auf Taf. IX abgebildeten mannlichen Tiere acht Kerne in der Epider- 

 mis und je zwei in den Lemnisken. 



It is interesting to observe that the foregoing statement as to 

 the number of nuclei is not put in general form but only indicates 

 that one individual possessed eight subcuticular nuclei. As the 

 result of the examination of several hundred individuals of the 

 genus Eorhynchus the writer has found but a single one in which 

 the arrangement and number of nuclei varied from the typical 

 condition of one ventral and five dorsal subcuticular nuclei. 

 This, in itself, would seem to indicate the the specimen which 

 Hamann was describing* was abnormal. Liihe ('04, p. 294), 

 commenting upon the works of Mtiller and Hamann regarding the 

 nuclei of the subcuticula, writes: "In der Figur Hamann's sind 

 freilich 6 Kerne in der Haut gezeichnet. Aber wenn die Zahl 

 dieser Kerne auch innerhalb gewisser Grenzen schwankt, so habe 

 ich doch gerade die von 0. F. Miiller gezeichnete Fiinfzahl verhalt- 

 nismassig haufig beobachtet und alsdann auch stets in der von 

 Mtiller gezeichneten Anordnung." 



These records, while of importance historically, cannot be re- 

 garded as infallible, primarily because in each case they were 

 made in the form of incidental observations rather than as ac- 

 curate determinations. The following paragraphs present the 

 results of my studies on subcuticular nuclei of five American 

 species. 



Eorhynchus gracilisentis. In this species the nuclei of the sub- 

 cuticula conform to so distinct a pattern, as regards numbers and 



