ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 593 



from tlio first in connection with the lateral cords, that the frontal 

 ganglion is formed from an unpaired invagination independent of 

 that which gives rise to the central nervous system ; (J) that the 

 dorsal canal described by Kowalevsky is an involution of the egg- 

 membranes ; (k) that the Malpighian vessels arise from the ectoderm 

 as diverticula of the hind-gut. 



The latter portion of Dr. Heider's memoir is occupied (I) with a 

 lucid exposition of the opinion that the various germinal layers are 

 derivable from the blastoderm which is superficially budded off from 

 the giant multinuclear trophodic yolk-cell, which thus occupies the 

 segmentation cavity. The gastrulation has the modified form of a 

 long furrow, the boundary between tbe two layers of the endo- 

 mesoderm represents the primitive enteric cavity, the margins of the 

 invagination form the stretched-out blastopore. The persistence of 

 nuclei within the yolk after the plastic elements have been differ- 

 entiated, may be connected with the delayed absorption of tho 

 former. While regarding the yolk as the passive trophodic remnant 

 comparable to that occupying the centre of a centrolecithally 

 segmented ovum, the author does not exclude the possibility of its 

 phylogenetic origin from modified endoderm segmentation masses, as 

 suggested by Kowalevsky' s report of what occurs in Euaxes. 



Behaviour of Dorsal Vessel during Metamorphosis.* — Prof. A. 

 Kowalevsky has studied in the larvae of Muscidse the behaviour of the 

 dorsal blood-vessel during the metamorphosis of the larva. In feed- 

 ing the larvae, for another purpose, with cochineal, silver salts, and 

 other colouring matters, he found that the pigment was passed in an 

 apparently uncoloured combination to special cells lying round the 

 heart, viz. (a) to the thirteen pairs of large cells lying posteriorly, 

 (b) to the band-like masses which surround it medianly, and (c) to 

 the anterior " garland-like strands " described by Weismann. Within 

 these cells the pigment, passed doubtless from the heart by the blood, 

 seems to enter into an insoluble combination with the plasma round 

 about the nucleus. Prof. Kowalevsky is therefore inclined to attribute 

 to these cells a blood-purifying function. 



The " garland-like strands " persist unchanged for two days after 

 metamorphosis, a fragmentation of the nucleus sets in, and the cells 

 gradually fall a prey to the fagocytes or granular spheres within 

 which the pigment again forms an uncoloured combination. The 

 strands therefore form an altogether embryonic or larval gland, which 

 does not pass on into the insect. 



He has shown that the anterior and median portions of the heart 

 completely pass over to the imago, and the cells enveloping the 

 middle portion also persist, changing their position, however, and 

 forming a broad mass of cells, which envelopes the anterior wall of 

 the abdomen as a thick network. They retain their introduced 

 pigment, and even in the adult insect these cells about the median 

 portion of the heart may be artificially fed with colour in similar 

 fashion. 



* Biol. CentralbL, vi. (1886) pp. 74-9. 

 Ser. 2.— Vol. VI. 2 R 



