596 SUMMABY OF CURRENT RESEARCHES RELATING TO 



dermo-muscular and entero-muscular layer. After describing the 

 stages of the development of these parts, the author points out that 

 (1) the mesoblast and endoblast are shown to have primitively a 

 common germinal layer, the various parts of which are only to be 

 distinguished by the diflference in the amount of yolk which they 

 contain. (2) In consequence of the wealth of yolk the enteric glandu- 

 lar layer is very slow in taking on the characters of an epithelium. 

 (3) The mesoblast of the Insecta is developed by being nipped off 

 from the endoblast, and the coelom is therefore primitively an entero- 

 ccele. 



Perfect State of Prosopistoma punctifrons.* — M. A. Vayssiere 

 points out the extreme interest which attaches to this rare Arthropod, 

 the systematic position of which has been a subject of so much doubt ; 

 doubts which were expressed by Milne-Edwards in his classical work 

 on the Crustacea. In 1869 Dr. Joly discovered the presence of 

 tracheae in the animal, and demonstrated the affinities of this insect 

 to the Ephemeridse. 



The author refers to the resemblances which in its development 

 the insect in question offers to the group just named, and says that its 

 aquatic period of life is characterized by the complete coalescence of 

 the thoracic somites with the anterior segment of the abdomen, and 

 the consequent diminution in number, and more complete localization 

 of the respiratory organs ; there are only five pairs of tracheo- 

 branchiae, and the first two of them have but a feeble respiratory 

 effect. After pointing out the characters of other genera, in which 

 there is also a certain reduction or localization of the respiratory 

 apparatus, M. Vayssiere shows that there is also a marked concen- 

 tration of the generative organs. The prothorax is intimately fused 

 with the metathorax, and the carapace thus formed gives rise to a 

 respiratory chamber, the water for which enters by two ventral 

 apertures and passes out by a single dorsal one ; this current is set 

 in motion by the first two pairs of respiratory organs. 



The nervous system is also concentrated ; in addition to the cere- 

 broid ganglion there is a single sub-oesophageal ganglion, and a very 

 large thoracic ganglion which represents by itself the whole of the 

 ganglionic chain. 



The subimaginal and imaginal stages appear during the month of 

 June ; the integument becomes of a darker colour, the two halves of 

 the carapace become separated, the head and thorax appear, while the 

 mouth organs disappear. Soon the abdomen is developed, and the 

 wings take on their definite form. 



An account is then given of the external form of the perfect insect, 

 and the author states that, as a result of his dissection of two females, he 

 foimd a large number of ellipsoidal ova, not unlike those of Gloe diptera; 

 the digestive canal was completely empty, and all its glandular organs 

 had entirely or partially disappeared. The nervous system was 

 as concentrated as in the nymph. The tracheal apparatus consisted 

 of two lateral trunks, which gave off a number of branches to the 



♦ Ann. Sci. Nat., xi. (1881) art. 1, 16 pp. (1 pi.). 



