( 272 ) 

 PEOGKESS OF MICEOSCOPICAL SCIENCE. 



Embryology of Insects. — Mr. A. S. Packard, jun., has furnished the 

 Peabody Academy of Science with a very valuable series of papers on 

 Diplax, Perithemis, and the Thysanurous genus Isotoma, M'hich have 

 just been published. The author enters fully on the development of 

 each insect, and illustrates his observations both by several woodcuts 

 and by a series of most valuable and carefully-drawn plates. He 

 states that in certain mites, as Hydrachna, Pontarachna, Thalassa- 

 rachna, and probably all the Hydi-achnidaj, the ocelli are situated over 

 the second pair of legs at a considerable distance behind the head. In 

 a genus of Annelids (Polyopthalmus) organs of sight are developed 

 on each ring of the body, or, as in certain Planarians, scattered irre- 

 gularly over the body. In the embryo of Isotoma and Diplax the 

 ocelli are evidently developed on the antennary segment, as they are 

 epithelial cells j^rimarily situated on the cephalic lobes, which seem 

 to form the tergite of the antennary segments. With this view, the 

 supposition he has expressed (led thereto by the generally-received 

 opinion of Milne-Edwards, Dana, and others, that the eyes of insects 

 and Crustacea represent limbs and therefore demand separate segments) 

 seems incorrect. Accordingly, he thinks we are forced to the belief 

 that the head of the hexapodous insects consists of but four segments, 

 i.e. the second maxillary, first maxillary, and mandibular segments, 

 situated behind the mouth-opening, and the antennary, or fii-st and 

 preoral segment, situated in front of the mouth. The cej)halic plates, 

 which fold back upon the head, forming the main expansion of the 

 insectean head, is apparently the tergum of the antennary segment. 

 The clypeus and labrum are apparently differentiated from the cejihalic 

 lobes, and thus seem to form a portion, or fold, of the antennary seg- 

 ment. These cephalic lobes in the Arachnids are described and figured 

 by Claparede as folding back on the top of the mandibular and maxil- 

 lary segments, bearing ocelli and forming the anterior w^all of the 

 mouth. The upper part of the head of an insect is, then, largely 

 tergal, rather than pleural as previously stated by him. 



Structure of the Bafs Wing. — This, which has long been a mystery, 

 has now been solved in an able paper by Dr. Joseph Schobl, of Prague. 

 According to him, the bat's wing membrane consists of two sheets of 

 skin, the upper derived from that of the back, the lower from that of 

 the belly. The epidermic and Maljtighian layers in each sheet remain 

 separate, whilst the true skin is inseparably fused. In this fused 

 medium layer are imbedded the muscles, nerves, vessels, &c., of the 

 wing. A complicated arrangement of delicate muscles is described, 

 which have their tendons formed of elastic tissue instead of the usual 

 white fibrous tissue. There are also present numerous long elastic 

 bundles stretched in different directions in different regions of the 

 wing. The arteries are each accompanied by a single vein and a 

 nerve, the three keeping company as far as the commencement of the 



