162 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Movements of Spermatids and their Parts.* — Dr. IvarBroman has 

 especially studied the spermatids in the dogfish and in man. Not only 

 the spermatids, but their more important cellular parts — to wit nucleus, 

 central corpuscle, and idiozom — exhibit regular movements, probably iu 

 response to various directive stimuli. Thus, the union of human sperma- 

 tids with Sertoli's cells is probably trophotactic ; the immigration of the 

 central corpuscles to the nucleus is a positive (perhaps polar) karyo- 

 taxis ; the central corpuscle exerts an attraction on the nucleus (positive 

 microcentrotaxis !) ; and so on. But the whole research leads one into 

 a somewhat rarefied atmosphere, in which tactic and tropic pheno- 

 mena are abundant — so abundant that the intruding reviewer cannot but 

 gasp. It is certain, however, that the author discloses an intricacy of 

 vital movement more complex than has been hitherto recognised. 



Tetrads in Spermatogenesis.! — S.Prowazek has continued by means 

 of Astacus, his work on this subject done previously on material obtained 

 from Helix and the rhinoceros beetle. As his new results complement 

 his previous ones, he gives figures showing the homologous stages in 

 the three types, and sums up his conclusions as follows : — The chromatin 

 first undergoes a division into fine dust-like particles, but this stage is 

 absent in the rhinoceros beetle ; it then forms a number of irregular 

 islands, from which the double chromosomes then develop ; from these 

 double chromosomes the tetrads are formed. In Astacus the raito- 

 chrondria are unusually well-developed, and their bel aviour shows that 

 they belong to the group of genetic or formative granulations, as distinct 

 from ergastic or functional granulations. 



Development of Teeth in Sus domestica.! — Dr. A. Bild finds that 

 the deciduous incisors are better developed in pig-embryos in the upper 

 than in the lower jaw, in which they are squeezed together. As to 

 prelacteal rudiments in the upper jaw, Id x has none, Id 2 has one which 

 has a very brief existence, early fusing with the tooth-rudiment, while 

 in connection with Id 3 in the same jaw there is a fairly well-developed 

 prelacteal epithelial-ridge which does not unite with the tooth-germ. 

 The thickening described by Adolf as a germ of a fourth incisor was 

 very plainly seen, and is due to the fusion of a prelacteal epithelial- 

 ridge with the dental ridge. The deciduous canine of the upper jaw has 

 connected with it a very well-marked prelacteal rudiment. Iu the lower 

 jaw all the deciduous incisors and the canine have prelacteal germs con- 

 nected with them, that of Id 2 being the best developed. The deciduous 

 molars have also prelacteal germs both in the upper and lower jaws, and 

 these fuse with the lacteal tooth-germs. Behind the last deciduous 

 molar both in the upper and lower jaw, the author finds a prelacteal 

 epithelial ridge which fuses with the tooth-ridge. The author entirely 

 contests the views of Wilson and Hill that this epithelial ridge is the 

 rudiment of the lip-furrow, and describes the development of the lip- 

 furrow which he regards as independent of the dental ridge. Further, 

 he believes that the tooth described by Wilson and Hill as the first 

 molar is really the last pre-molar. The author is of opinion that his 



* Arch. f. Mikr. Anat., lix. (1901) pp. 106-43 (59 figs.), 

 t Zool. Anzeig., xxv. (1901) pp. 27-9 (16 figs.). 

 % Anat. Anzeig., xx. (1902) pp. 401-10 (12 figs.). 



