ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 075 



observed, but probably in the species of spicier upon which the most 

 complete observations were made, two pairs of abdominal feet are 

 involuted. 



Whether the conversion of the abdominal feet into the lung-book 

 is to be regarded as an involution of certain paired appendages, as 

 was suggested by Lankester on theoretical grounds, or as a portion 

 of the abdomen over which an appendage corresponding to the oper- 

 culum of Limulus extends, could not be positively determined. 



There appears, from one series of sections, to be a swelling corre- 

 sponding in position to the operculum of Limulus just in advance of 

 the involuted abdominal appendages. 



Another point of interest in Arachnid embryology is the presence 

 of a fold in the blastoderm, surrounding the cephalic region of the 

 embryo. Balfour described this fold as a groove. It appears, how- 

 ever, when studied by transverse and longitudinal sections, to be a 

 fold of the blastoderm. At the anterior extremity of the fold its 

 opposite sides unite over the median line of the embryo, so that the 

 brain is partially invested by an outer sheath or bag of epiblast 

 formed by the united inner limbs of the opposite sides of the fold. 



The origin of this fold and the union of its opposite sides over the 

 middle line of the embryo correspond to the amnion of insects. The 

 difference between the insect amnion and the spider amnion, lies in the 

 fact that in the former the union of the opposite sides of the amniotic 

 fold is in most cases complete throughout the length of the embryo, 

 while in the latter folds are developed only in the head region of the 

 embryo and coalesce at their anterior ends. 



Psychical Development of Spiders.* — Herr J. Dahl communi- 

 cates the results of some observations on the psychical development 

 of spiders. By means of the sensory organs on the palps and limbs, 

 the spiders discover not only the capture of an insect in the web, but 

 the place where it is. Atius arenatus was unmistakably influenced by 

 loud knocking. The same species can distinguish a moving object of 

 the size of a fly at a distance of about 20 cm. Distinct vision begins, 

 however, at 2 cm., but then so exactly that the legs of the fly can be 

 distinguished. Beyond the above limit the vision is very indistinct. 

 The above species and Xysticus Junto could distinguish colours very 

 imperfectly, but Epeira cornuta and Drassus quadripunctatus exhibited 

 this aptitude. A male Epeira patagiata was able to perceive various 

 odours and to distinguish them. Thomisidse were but slightly 

 sensitive to odours, but Attidse very much so. 



Eyes of Spiders.f — Prof. P. Bertkau adds to the numerous recent 

 researches on the eyes of Arthropods, an account of those of spiders. 

 Ibis is based on an investigation of Micrommata virescens, Dolomedes 

 limbatus, several Thomisidaa, Epeiridae, &c, but, without entering into 

 the detailed peculiarities of the different genera, it will be enough to 

 summarize his general results. 



* Vierteljahresschr. f. Wiss. Phi]., ix. Cf. Arch. f. Naturgesch., lii. (18S6) 

 p. 83. 



t Arch, f Mikr. Anat., xxvii. (1886) pp. 589-631 (2 pis.). 



