524 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Arthropoda. 

 a. Insecta. 



Maturation in the Eggs of Hive-Bees. * — A. Petrunkewitsch has 

 made a careful study of this, and believes that he has securely established 

 or confirmed the following conclusions. Eggs laid by the queen in 

 drone-cells are always unfertilised. As in the fertilised ova, the first 

 polar body is separated off by an equation-division. In the separation 

 of the second polar body there is in all cases a reduction of the number 

 of chromosomes to one-half. Similarly the first polar body always 

 divides with a reduction, and the peripheral half is liberated from the 

 ovum and perishes. The restoration of the number of chromosomes in 

 the non-fertilised ova probably occurs by longitudinal splitting of the 

 chromosomes, but with suppression of the corresponding division into 

 two daughter-nuclei. The central half of the first polar body conjugates 

 regularly with the second polar body, and thus arises a Richtungs- 

 copulationskem with the normal number of chromosomes. This nucleus 

 (in the egg which develops into a drone) gives rise, by three divisions, to 

 eight cells with " double " nuclei. Tn fertilised ova, and also in the 

 " drone eggs " of fertile workers, the aforesaid nucleus forms a spindle, 

 which either simply disupj^ears, or gives rise to a number of cells (1-4). 

 But these always show disruptive phenomena in the chromatin, and 

 ultimately perish. 



Endoderm of Insects, f — Dr. K. Escherich discusses the difficult 

 question of the formation of the germinal layers in insect development, 

 and concludes that the process is not essentially different from what 

 occurs elsewhere. The differentiation of the two primary germinal 

 layers takes place either by invagination or by immigration. When 

 the endoderm-cells lose their connectedness and wander from their seat 

 of origin into the yolk, then the mid-gut arises by a meeting of these 

 " yolk-cells " on the surface of the yolk, a process observed in Lepisma, 

 Aphides, and Phryganidae. But if the endoderm-cells formed by 

 gastrulation at the two poles remain in connection, then the mid-gut 

 wall arises by proliferation from the two endoderm primordia. In this 

 bipolar foundation of the endoderm the development of insects is 

 unique, but not otherwise, and the peculiarity may be interpreted as a 

 special adaptation to the form of the egg and the amount of yolk. 



Nerve-Endings in Butterflies' Wings. £ — Dr. K. Giinther has fol- 

 lowed the branching of the nerve which enters the wing. In many 

 cases a fine end of a branch was seen to run into a specialised mono- 

 nuclear cell, from which a process passes through a pore in the chitin 

 to the base of but not into a scale. Thus the scale may have structural 

 connections exactly similar to those of the well-known integumentary 

 sensory hairs. 



The author describes glandular scales, glandular hairs, sensory 

 spines, and sensory cupolas. While some scales are glandular and 

 others sensory, it may be that all are innervated. Thus in Pieris napi y 



* Zuol. Jahrb.. xiv. (1901) pp. 573-608 (4 pis. and 1 fig.), 

 t Biol. Ceutralbl., xxi. (1901) pp. 410-31 (14 figs.). 

 % Zool. Jahrb., xiv. (1901) pp. 551-72 (1 pi.). 



