522 SUMMARY OF CURRENT RESEARCHES RELATING TO 



nuclei, which wore not previously found in the glia-cells, are quite 

 distinct if the preparations be not too deeply stained. Further, the 

 characters of the glia-fibrillaa, as shown by his new preparations, are 

 such as to bring his results more into line with those of Apathy for 

 Hirudinege. 



Spermatogenesis in Helix pomatia.* — S. Prowazek describes and 

 figures the various stages in development of the spermatozoa of this 

 species. The spermatogonia cluster in a grape-shaped fashion round the 

 large basal cell, which is probably nutritive in function. The normal 

 number of chromosomes, as shown by other authors, is twenty-four. In 

 the division which forms the spermatocyte of the first order, the twenty- 

 four chromosomes which first appear in some cases show a longitudinal 

 splitting, and the forty-eight elements so formed unite in tetrads, so that 

 the number is reduced to twelve. In the second spermatocyte division 

 these twelve chromosomes split transversely, so that the daughter-cells 

 have each twelve. The tetrads were only made out in rare cases. 



With the conditions seen in Helix the author contrasts those found 

 in the beetle Oryctes nasicornis, in which he has also studied the develop- 

 ment of the spermatozoa. 



Nervous System of Capulus hungarieus.f — The late Prof. Henri de 

 Lacaze-Duthiers found that this Gastropod belongs to his type Strepsi- 

 neura aponotoneura, the ganglia called pleural and pallial being close to 

 the cerebral ganglia, and therefore displaced to the dorsal region, so 

 that the commissure, which is twisted from its point of origin, also arises 

 dorsally. Owing to the proximity of the cerebral ganglia, the sub- 

 cesophageal commissure hardly exists at all. The pedal ganglia, here 

 as always, are paired symmetrically; they are not near the pallial 

 ganglia. In addition to the pallial ganglia, there are present four pairs 

 of ganglia corresponding to those usually called sub-intestinal and 

 visceral (here paired) ; but to these and the pallial ganglia the author 

 preferred to give the general name of asymmetrical centre. This asso- 

 ciation of ganglia is always asymmetrical, even when, as in the present 

 instance, all the ganglia are paired, and the author regards its dis- 

 sociation into separate centres as a matter of great difficulty from the 

 point of view of comparative anatomy. In Capulus this asymmetrical 

 centre, in addition to the typical live ganglia, contains an accessory 

 ganglion near the visceral ganglion. 



Anatomy and Phylogeny of Chitonidge.J — Prof. Ludwig H. Plate, 

 in continuation of his work on this subject, discusses the families 

 MopaLiidae, Acanthochitidre, and Cryptoplueidae, and sums up his re- 

 searches in a general account of the structure, with a discussion of the 

 origin and relationships. Some of the more general of his conclusions 

 may be stated as follows. In the Chitons in general the degree of 

 specialisation seems to bear a definite relation to the size of the body, 

 the larger forms having always a more elaborate structure than the 

 smaller. The size again appears to be related to the habitat, the largest 



* Arbeit. Zool. Inst. Wien, xiii. (1901) pp. 197-236 (2 pis. and 2 figs.). 



t Arch. Zool. Exper., ix. (1901) pp. 43-79 (1 pi.). 



X Zool. Jahrb., Supp. v. vol. ii. (1901) pp. 2S1-600 (5 pis.). 



