486 SUMMARY OF CURRENT RESEARCHES RELATING TO 



spleen always arises as a dense aggregate of mesenchyme cells with 

 simultaneous co-operation on the part of the proliferating coelomic 

 epithelium. He maintains that the spleen is purely mesodermic, without 

 direct developmental association with the dorsal pancreas or with any 

 endoderm. E. Glas has maintained that in the grass-snake, the ^ origin 

 of the spleen is distinctly endodermic, and bound up with the origin of 

 the dorsal pancreas. 



Examination of embryos of this snake leads Tonkoff to reaffirm 

 his conclusion. In this case also the spleen arises from a mesenchyme 

 aggregate, quite independently of the dorsal pancreas, with which it is 

 secondarily connected. 



Development of Teeth in Selachians.* — P. Laaser finds that a 

 ■dental ridge appears very early in embryos (3-4 cm. in length) of 

 JSpinax, Acanthias, and Mustdus, as a slight thickening of the epithelium 

 with a subjacent mesenchyme thickening. In embryos of Spinax and 

 Acanthias it appears earlier in the lower jaw ; in embryos of Mustelus 

 it appears earlier in the upper jaw. 



Not only do the teeth arise on the dental ridge, but the outer dental 

 epithelium shares directly in their formation exactly after the fashion 

 of placoid scales. At the margin of the outer dental epithelium there 

 is a groove (the external marginal-groove) which must not be confused 

 with the lip-groove. 



The first teeth-rudiments appear on the transition area from external 

 dental epithelium to dental ridge. They are developed earlier than 

 those on the external dental epithelium or those on the dental ridge. 

 The first hard substance to be formed is dentine ; the enamel covering 

 is not to be seen in the early stages. Very early there appears to 

 the inside of the dental ridge, above and below, an inturned fold of the 

 buccal mucous membrane, — the internal mouth-fold. This afterwards 

 forms the internal margin of the buccal cavity. 



Preputial Glands of Rabbit.f — Dr. Courant has made a study of 

 the glandulge prteputiales and the changes which they exhibit. There 

 is a " white gland " which is merely an aggregated sebaceous gland, and 

 a "brown gland" which is peculiar, and morphologically nearer the 

 sudorific type. The brown preputial gland exhibits periodic changes, 

 which are described. The changes are in all probability associated with 

 the period of rut, but the evidence is not quite conclusive. Courant 

 regards their function as conducive to sexual attraction by the secretion 

 ■of a strongly smelling substance. 



Non-Existence of " Neutrophil " Granulations in Leucocytes of 

 Man and Monkey.} — E. Marino finds that Ehrlich's classification of 

 the leucocyte-granulations in the blood of man and monkeys is not 

 altogether verifiable. Ehrlich distinguished (a) eosinophil or oxyphil 

 granulations staining with acid stains, (b) basophil or nietachromic 

 granulations which take on basic stains, and (c) neutrophil granulations 

 which will stain only in neutral mixtures. But Marino finds that the 



* Jenaieche Zeitschr. f. Naturwiss., xxxvii. (1903) pp. 551-78 (1 pi. and 13 figs.). 

 t Arch. Mikr. Anat., lxii. (1903) pp. 175-93 (2 pis.). 

 X Ann. Inst. Pasteur, xvii. (1903) pp. 357-64 (1 pi.). 



