ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 633 



V-shaped Centrosomes. * — Dr. K. v. Korff has found these in 

 spermatocytes of various beetles, e.g. Hydropliilus, Feronea. As they 

 were originally described by Meves in the mule genital cells of a butter- 

 fly, it is possible that they are widely spread in Insects. In beetles 

 they were found in the spermatocytes of the first order, and were of 

 large size. The two halves were originally at an angle of 90°, and the 

 two centrosomes separated by a greater or less distance; but at the 

 beginning of the first mitosis they separated from one another and 

 travelled to the poles of the nucleus. Later, each V splits into two 

 rods, the halves travelling in the daughter-cells to opposite poles. 

 These rods form the centrosomes of the second maturation division. 

 Similar V-shaped centrosomes were found in the spermatocytes of the 

 first order in the domestic duck, aud formed rods in the second division 

 after a similar fashion. 



Cephalic Mesoblast in Larus ridibundus. | — H. Rex finds that in 

 early embryos the mesoderm in the region of the auditory pit segments 

 into two parts, the dorsal and the ventral mesoderm. The ventral 

 portion gives rise to the so-called connecting-plate (Verbingdungsplatte), 

 and the heart primordium; the dorsal to the mesoderm of the hyoid 

 arch. In the earlier stages of development, the dorsal and ventral 

 mesoderm of the mandibular region are distinctly separated, but this 

 distinct limitation is lost in the later stages. The mesoderm of the 

 mandibular arch, from which the trigeminus muscle arises, is in direct 

 connection with the primordium of the heart. On the other hand, the 

 mesoderm of the hyoid arch, from which the facial muscle arises, 

 originates only from the connecting-plate, and has no connection with 

 the future heart. 



Development of Shoulder-Girdle in Bird?. % — Dr. Wlodzimierz 

 Kulezycki's observations on this subject have led him to the conclusion 

 that the clavicles in birds are not, as has been supposed, preformed in 

 cartilage, nor is there, as Gegenbaur stated, a strip of cartilage in the 

 embryonic clavicle. The author fails to find any pre-existing cartilage 

 at all, and believes that the clavicle is purely a dermal bone, which can- 

 not be homologised with the whole clavicle of mammals, for it only 

 corresponds to the dermal element of that bone. In the bird, clavicle, 

 coracoid, and scapula arise from a common primordium, but the clavicle 

 becomes differentiated early, and ossifies without the intervention of 

 cartilage, while the other two bones arc preformed in cartilage. 



Development of Nostrils in Lizard § — Dr. Karl Peter, in his study 

 of embryos of Lacerta, found the peculiar swelling in the vicinity of the 

 neuropore, which Ko Hiker described in various gnathostomate verte- 

 brates, aud homologised with the swelling in the cyclostomes from 

 which part of the unpaired nostril arises. Peter followed the changes 

 undergone by this "unpaired olfactory organ" of Kolliker, with a view 

 to deciding the question of its homologies. He finds that the structure 

 arises during the closing of the neuropore, and speedily undergoes 

 degeneration. It does not possess the characters of a sensory plakode, 



* Anat. Anzeig., xix. (1901) pp. 41)0-3 (7 fi^s.). 



t T«>m. cit., pp. 417-27 (15 fi-s.). t Tom cit., pp. 577-90 (3 figs.). 



$ Arcli. Mikr. Anat.. lviii. (l'JOl) pp. 640-60 (1 pi.). 



