66 SUMMARY OF CURRENT RESEARCHES RELATING TO 



organized (neuroptera) forms in palaeozoic strata ; the absence of any 

 primitive forms tending to unite the existing orders, &c. He proposes 

 to divide the hexapoda into two classes : — 1. Apteryogenea, and 

 2. Pterygogenea ; the latter he divides into sixteen orders, based on 

 the structure of the gnathites, instead of the existing six orders. 



S. Araclinida. 



Duration of Life in Spiders.* — Herr F. Dahl in reply to the 

 criticisms of Dr. Bertkau and Dr. Karsch,f states that he proved to be 

 a certainty the seasonal dimorphism of Meta segmentata, which was 

 only rendered probable by the investigations of other naturalists. 

 The main aim of his paper was, however, to direct the attention of 

 naturalists to other species, such as Micrommata viriscens, of which 

 Dahl himself could not obtain specimens. With regard to the 

 duration of life of spiders, it was pointed out that in the majority of 

 spiders, particularly the males, the season of sexual maturity was 

 always definitely fixed ; and this fact appears to point to a very short 

 span of life in these species ; moreover, in certain seasons no in- 

 dividuals whatever of some species can be found — which further 

 supports the same conclusion. 



Embryology of Limulus.^ — Dr. J. S. Kingsley was unfortunately, 

 unable to study the earlier stages in the development of Limulus, but 

 he comes to the conclusion that the yolk is wholly hypoblast, and 

 that the primitive groove is the homologue of the blastopore. The 

 history of the development of the mouth seems to show that the 

 functional mouth is not a strictly homologous structure throughout 

 the animal kingdom, but that in those forms with a mouth it has been 

 considerably modified in position. The history of the "brick-red 

 glands " with the corresponding ones in the scorpion, and the so- 

 called shell-glands of Crustacea, leads the author to regard them as 

 segmental organs. The abdominal appendages are from the first 

 broad and leaf-like, and so differ from the corresponding limbs of 

 Arachnids. 



The nervous system first appears as two longitudinal epiblastic 

 thickenings, one on either side of the middle line ; there is no external 

 neural groove, but one on the inner surface of the cord ; this is doubt- 

 less due to the egg filling its envelope so completely that an inward 

 bending is impossible. The commissural portions are separated from 

 the epiblast before the ganglionic areas. The brain is at first separate 

 from the rest of the nervous system ; it arises as two halves, each of 

 which has a marked similarity to those of spiders. 



The study of the development of Limulus has convinced Dr. 

 Kingsley of the Arachnidan affinities of this animal, but its relation- 

 ship to the Phyllopoda is also marked ; it is a " synthetic type." He 

 regards the eyes of all Arthropods as really specialized portions of 

 the epiblast of the head, and as having a common phylogenetic origin 



* Zool. Anzeig., viii. (1885) pp. 629-31. 



t See this Journal, v. (1885) pp. 993 and 994. 



X Quart. Journ. Micr. Sci., xx^. (1885) pp. 521-76 (3 pis.). 



