34 SUMMARY OF CURRENT RESEARCHES RELATING TO 



walls of which are separated from the vitelline membrane by a thick 

 layer of yolk ; it is inclosed in a thin layer of protoplasm with nuclei 

 which represents the ectoderm. Along one line there is a prominent 

 ridge on the outer side of the ectoderm, composed of proliferating 

 nuclei ; anteriorly this ridge divides into two, which remain attached to 

 one another above and below, and so inclose a cavity between them. 

 The praeoral lobes next appear ; not far from the anterior end of the 

 embryo tbe yolk is divided by a protoplasmic septum, which divides the 

 body of the embryo into two sacs, one lying above the other ; posteriorly 

 these two sacs communicate. By the ingrowth of the surrounding tissue 

 the septum becomes divided into two layers, and the embryo now con- 

 sists of a sac doubled on itself in such a way that the ventral face of the 

 anterior part of the body is opposed to that of the posterior part. The 

 embryo nest begins to straighten itself out ; in the anterior region the 

 somites are represented by a series of definite cavities at the side of the 

 body, and, later on, they appear throughout the whole length of the 

 embryo. When the peripheral food-material has been completely 

 absorbed the embryo lies just within the vitelline membrane and egg- 

 shell. Along a lateral ridge the appendages begin to appear as blunt 

 rounded protuberances ; the antennaa arise as buds on the prasoral lobes. 

 The nerve-cords first arise as special rounded elements at the internal 

 ventral angles of thickenings of the ectoderm over the leg-ridges. 



S. Araclinida. 



Acarida on Trees.* — Herr C. "W. S. Aurivillius was prompted by the 

 researches of Dr. Lundstrom on " doroatia " (see infra, p. 87) to in- 

 vestigate the nature and behaviour of some of the Acarid guests which 

 abound on the leaves of trees. He describes in detail the structure and 

 mode of life of three forms — Tydeus foliorum, Gamasus vepallidus, and a 

 third, found as nymph and larva, and apparently an Oribatid, very like 

 Cepheus tegeocranus. All the three were found on leaves of Tilia. From 

 observation, and from a study of their mouth-parts, the author was con- 

 vinced that these guests could not derive their food from sucking wounds 

 which they might not unnaturally be supposed to make on the leaves, 

 nor did Tydeus appear to attack the Aphides. They more probably 

 live on small solid particles, not due to their own exertions, but such for 

 instance as fungoid spores. 



e. Crustacea. 



Development of the Compound Eye of Crangon-t — Dr. J. S. 

 Kingsley, who has already published a preliminary notice on this sub- 

 ject,! now gives full details as to his observations on the development 

 of the compound eye of Crangon. 



The compound eyes begin to make their appearance soon after the 

 closure of the blastopore : there is a shallow pit, which rapidly grows 

 deeper, and, extending outwards, downwards, and forwards, soon conies 

 to occupy a position beneath the anterior and outer part of the optic 

 disc before any striking changes are visible in the external appearance 

 of the embryo. The separation of the pit from the epiblast is completed 

 at about the time of budding of the first pair of appendages, and the 



* Nova Acta Soc. Sci. UDsala, xiii. (1887) pp. 1-16. 

 t Journ. of Morphology, "i. (1887) pp. 49-64 (1 pi.). 

 J See this Journal, 1387, p. 84. 



