Febeuaet 17, 1911] 



SCIENCE 



273 



species are relatively common in Europe. During 

 the past summer, a form belonging to this group 

 was found in fish from the Illinois River at 

 Havana. Its structure shows certain features 

 which are common to both of the linown genera, 

 Garyophyllceus and Archigetes. It resembles the 

 former in the absence of a caudal appendage and 

 in the location chosen by the adult parasite, viz., 

 the intestine of a fish, whereas, so far as known 

 in Europe, Archigetes always possesses a tail and 

 has been found only in the body cavity of tubi- 

 ficid worms. In general appearance and structure 

 the American form resembles the European Archi- 

 getes very strongly. It has a scolex of fixed form 

 with primitive suckers or phyllidia and also the 

 musculature of Archigetes. The general arrange- 

 ment of reproductive organs, especially the two 

 rows of testes in the central field, and the genital 

 pores, correspond also closely to conditions in 

 Archigetes. Two alternative hypotheses present 

 themselves: (1) the European forms may have 

 a yet undiscovered adult stage in some vertebrate 

 host and in that case the caudal appendage would 

 be lost as in Garyophyllceus and in the form 

 under discussion; (2) the American form de- 

 scribed here may represent a higher stage of 

 development. In the latter case the European 

 form is either a degenerate type in which the 

 intestinal stage has fallen out of the life history, 

 leaving only a sexually mature larva parasitic in 

 the body cavity, as Amphilina another cestodarian 

 has been interpreted by Pintner; or the American 

 form indicates the adaptation by which the inver- 

 tebrate parasite has acquired a vertebrate host 

 and includes in its life history two hosts, as is 

 typical in cestodes generally. The full paper will 

 be published elsewhere. 



Notes on Extinct Amphibia: Roy L. Moodie, Uni- 

 versity of Kansas. 

 Chromosome Individuality : C. E. McClung, Uni- 

 versity of Kansas. 

 'The Histogenesis of the "Transient" (Rohon- 

 Beard) Cells in Selachian Embryos: H. V. 

 Neal, Knox College. 



The study of the histogenesis of the " tran- 

 sient" (Rohon-Beard) cells in selachian embryos 

 confirms earlier conclusions based upon the study 

 of the histogenesis of ventral nerves that the 

 neuraxon process develops as an amoeboid outflow 

 of the neuroblast cell. The growth and histo- 

 genesis of the neuraxon process of the " tran- 

 sient " or " giant " cells of Rohon-Beard may be 

 easily followed, since in reaching its peripheral 

 termination the process grows into and through 



spaces devoid both of mesenchyma cells and of 

 intercellular bridges or " plasmodesmata." Such 

 spaces, however, are filled with a plasma contain- 

 ing a slight amount of coagulable substance 

 which with some fixing reagents gives the plasma 

 a vacuolated structure. The termination of the 

 nerve fiber or neuraxon, as it penetrates these 

 spaces, consists of many pseudopodia-like exten- 

 sions. In some cases, as the neuraxon in its 

 growth reaches the dorsal apex of the myotome, 

 pseudopodial processes extend, some median and 

 some lateral to the myotome. It seems to be a 

 matter of chance whether in its fxirther extension 

 the neuraxon process shall grow median or 

 whether it shall grow lateral to the myotome. 

 Of a primary reticulum or " plasmodesma " con- 

 necting the neuroblast cell in the neural tube 

 with its terminal organ there is not the slightest 

 evidence. The experimental results of Harrison 

 on amphibian embryos are fully corroborated by 

 the evidence presented by the growth of the neu- 

 raxon processes of these " giant " cells. 



Such facts obviously have an important bearing 

 on the problem of the phylogeny of the vertebrate 

 head, since they tend to disprove the assumption 

 of earlier morphologists that nerve and muscle 

 are inseparably connected and to make explicable 

 the greatly modified metameric relations of the 

 eye muscle nerves and possibly to give us the clue 

 which may lead to the solution of the mystery of 

 the chiasma of the trochlearis. 



The Origin of the Rudiments of the Mesenteron 

 in the Honey Bee: James A. Nelson, Bureau 

 of Entomology, Washington, D. C. 

 The anterior mesenteron rudiment of the honey 

 bee arises at a period immediately after the 

 appearance of the lateral folds, on the ventral 

 surface of the egg near its anterior pole. It is at 

 first nearly circular in outline, and sharply dis- 

 tinguished from the blastoderm by the deeper 

 staining properties of its cells. At first it lies 

 outside the area embraced by the lateral folds, 

 but is later included in this area as the folds 

 lengthen. Sections show that this mesenteron 

 rudiment is produced by active proliferation of 

 the cells of the blastoderm. After the union of 

 the lateral folds this is detached from the blasto- 

 derm as a flat plate of cells which increases 

 rapidly in extent, moves cephalad and soon covers 

 the yolk at the anterior pole of the egg like a 

 cap. The history of the posterior mesenteron 

 rudiment is similar, but it is smaller, and first 

 appears at the posterior pole of the egg. Later, 

 after the rudiments of the appendages have ap- 



