ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 157 



INVERTEBRATA. 



Arthropoda. 

 a. Insecta. 



New Cavernicolous Podurid.* — K. Absolon describes Acherontiella 

 omjcltiuriforinis g. et sp. n., ti minute snow-white member of the order 

 Collembola, from caves at Algiers. It resembles Omjchiurus in form. 

 There is a noteworthy absence of biting moutli-parts, eyes, leaping 

 organ, postanteunary organ, anal papilla, anal spines, and empodial 

 appendage. It is an archaic form Avith striking negative features. 



Development of Aptery^ota.f — Jur. Philiptschenko gives an 

 account of the development of Isotoma cinerea, one of the Collembola. 

 He describes the segmentation, the formation of the blastoderm and 

 yolk-cells, the early segregation of the gonadial primordia, the establish- 

 ment of the layers and the germinal disk, the formation of the dorsal 

 organ and the envelopes, and the organogenesis generally. 



It appears to be the rule among Insects that the genital cells are 

 set apart before the differentiation of the germinal layers, but in some 

 cases they do not become recognizable until somites are established. 



The yolk-cells of Insects and other Arthropods are not to be regarded 

 as endodermic, or as in any relation to the germinal layers. They are 

 cleavage-cells which remain in the yolk and prepare it for absorption. 

 They do not share in forming the embryo. 



It seems most convenient to speak of two primary germinal layers, 

 the ectoderm and the lower layer. From the latter arise the composite 

 " primitive primordia " of the somites, etc. The dorsal organ is quite 

 independent of the embryonic envelopes ; it is probably an embryonic 

 excretory organ ; the envelopes arise from the part of the blastoderm 

 which is not involved in forming the body. 



Corpora allata of Insects. J — Arthur Nabert has studied these 

 bodies associated with the pharyngeal ganglia in the head, neck, and 

 anterior thorax. They occur in all Insects, and are first paired, then 

 unpaired. They are spherical, ellipsoidal, or oval, and usually smaller 

 than the pharyngeal ganglia. Each is surrounded by a mesodermic 

 envelope, continuous with the perineurium of the ganglion. They take 

 on stain intensely, and show vacuoles and many small nuclei, or a few 

 large ones. They are innervated from the pharyngeal ganglia. Their 

 development, the glandular vacuoles, the dark staining of their matrix, 

 and the richness in chromatin point to their being glands of internal 

 secretion. 



Rod-like Central Corpuscles in Insects.§ — S. Tschassownikow 

 has studied these in the spermatogenesis of water-beetles, Dytiscus 

 marginalis and Hydrophilus piceiis, and comes to the following conclu- 

 sions. 1. The rod-like central corpuscles, which consist of a row of 



* Arch. Zool. Exper., li. (1913) pp. 1-7. 



t Zeitschr. wiss. Zool , ciii. (1912) pp. 519-660 ^5 pis.). 



X Zeitschr. wiss. Zool , civ. (1913) pp. 181-358 (5 pis. and S figs.). 



§ Arch. Mikr. Anat., Ixxxi. (1913) 2te Abt., pp. 73-86 (2 pis.). 



