ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 647 



insects or parasites, the concentration of the central nervous system into 

 one or two masses, the presence of a sucking stomach, and the reduction 

 of the malphigian tubes to a small number, or a remarkable increase of 

 the same, etc. Amongst such are also to be included viviparous forms 

 in the most different groups, polymorphism, formation of states, the 

 origin of resting stages (pupa), and of similar larval forms in otherwise 

 very different groups. The Holometabola, it can scarcely be doubted, 

 form a convergent group, and are really heterophyletic. In judging and 

 valuing characters in classification, it is well to keep in view the fact that 

 biologically important characters may be unimportant taxonomically. 



Metamorphosis of Central Nervous System in Insects.* — V. Bauer 

 finds that the formation of the central nervous system is not completed 

 at hatching. A post-embryonic development takes place which is con- 

 tinuous in the forms without metamorphosis, original in the Metabola. 

 For the new formation of ganglia, special centres, consisting of neuro- 

 blasts, are present. Ganglionic cells arise by two divisions. The first 

 division of the neuroblast leads to the formation of two different part- 

 products, of which the one becomes a ganglion mother-cell, whilst the 

 other, retaining the neuroblast character, repeats the division. The 

 ganglion mother-cells, by simple division, give rise to ganglion cells. 

 Ganglion cells, as well as connective tissue and tracheae of a provisional 

 character, degenerate partly with and partly without the aid of phago- 

 cytes. 



Nutritive Role of Follicular Epithelium in Melolontha vulgaris.! 

 Th. Mollinson finds that the terminal ovarian chamber contains only 

 oocytes and young epithelial cells, and that it is only the latter which 

 have to do with the nourishment of the growing ovnm. In perform- 

 ing this function they may, it is true, sometimes utilise the debris of 

 superfluous oocytes. 



The activity of the epithelial cells finds expression not only in the 

 formation of pseudopodia-like processes which penetrate into the ovum, 

 but also in the formation of nutritive strands and, in some cases, of 

 a nutritive reservoir around the ovum. There is also on the part of the 

 ovum an active role in the formation of its cytoplasmic substances. 



In Geotrupes stercorarlus there are similar arrangements, but a central 

 protoplasmic process formed by the ovum persists in addition to the 

 reservoir and nutritive strand formed by the epithelial cells. 



Muscle-Changes in Beetle (Thymalus marginicollis) during 

 Metamorphosis.:}: — R. S. Breed finds that some of the larval muscles 

 remain unaltered during metamorphosis, a few degenerate, while many 

 metamorphose into imaginal muscles. Imaginal muscles are formed in 

 the pupa from cells of an embryonic nature, but they are few in number. 

 Those undergoing no change are all found in the abdominal region, the 

 typical degenerating forms in the thorax and first and last abdominal 

 somites. The muscles of new formation were observed in only two 



* Zool. Jahrb., xx. (1904) pp. 123-52 (2 pis.). 



t Zeitschr. f. wiss. Zool., lxxvii. (1904) pp. 529-45 (2 pis.). 



X Bull. Mus. Zool. Harvard, xl. (1903) pp. 317-82 (7 pis.). 



2 Y 2 



