632 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The author is of opinion that the synaptic state is merely the ex- 

 pression of a more intimate relation between archoplasm and nucleus, 

 and it is probable that this relation becomes less close as soon as the 

 chromatic rings are constituted. Further, he does not believe that 

 during the growth-period of the spermatocyte, the chromatic elements 

 undergo a simple growth : rather they exhibit a radical transformation, 

 probably involving a new formation of chromatin. 



Development of Striped Muscle.* — E. Godlewski finds that, in mam- 

 mals, the myoblasts can be distinguished from the other cells by their 

 granular nature. At the time of their conversion into muscle-cells, 

 the myoblasts become elongated, and the granules arrange themselves 

 in longitudinal rows, thus forming very fine primitive fibrillar. The 

 transverse markings on these fibriUae are due to processes of differential 

 growth. In heart-muscle, the fibrillae are absolutely independent of the 

 cell-territories. Increase in the number of fibrilla> is probably due to 

 the longitudinal splitting of the primitive ones. 



Development of Teeth in Sus scrofa.f — Dr. P. Adloff finds that in 

 the domestic pig the first premolar becomes differentiated at the same 

 time as the other milk-teeth, but lags behind the others, and becomes 

 the last member of the milk-dentition to be developed. In the lower 

 jaw, in connection with the first premolar, there are two rudimentary 

 tooth-germs. If this premolar is regarded as a member of the per- 

 manent dentition, then these two rudiments must be looked on as a 

 rudimentary milk-jiredecessor and a pre-lacteal germ. If, as the author 

 inclines to believe, the first premolar is itself a milk-tooth, then both 

 these rudiments must be regarded as pre-lacteal germs. Pre-lacteal 

 germs were also found in connection with the second upper and the 

 first lower incisor. An interesting jioint is the development of a tooth- 

 germ behind the third incisor, which appears to fuse with that tooth, 

 and perhaps represents an ancestral fourth incisor. The author regards 

 these results as proving that concrescence is no longer a hypothesis, but 

 a fact demonstrable in the ontogeny. 



Tooth-genesis in the Caviidsp.^ — H. W. Marett Tims has cut sec- 

 tions of the jaws in a number of foetal guinea-pigs. He believes that 

 the five posterior tooth-germs (cheek-teeth) all belong to the permanent 

 scries, the first and fourth having vestigial remains of milk predecessors 

 in the shape of spherical clusters of cells, the concentric bodies. The 

 second tooth-germ forms the deciduous molar, shed before birth, and not. 

 replaced, though the first cheek-tooth drops backwards and occupies its 

 position. From the pattern of this deciduous tooth, the author regards 

 it as the first of the so-called molar series ; but his discovery of the milk 

 rudiments mentioned above tends to break down the distinction between 

 molars and premolars, and to show further that the molars belong to the 

 permanent dentition. No evidence of a pre-milk dentition was found. 

 His results in regard to the cusps of the cheek-teeth tend to confirm 

 the author in his view that the Rodentia arc derived from the Multi- 

 tuberculata. 



* Bull. Interna*. Acad. Soi. Cracovie. 1901, pp. 1-!C»-5S (1 pi.). 



t Anat. Anzeig., xix. (1901) }>p. 481-90 (6 figs.). 



; Journ. Linn. See. (Zoo!.), xxviii. (190]) pp. 1^01-00 (7 pis. ami 1 fig.). 



