746 SUMMARY OF CURRENT RESEARCHES RELATING TO 



incomplete. The neurilemma is a very thick, hyaline membrane, which 

 almost always breaks away from sections, and so escaped the notice of 

 Balfour. The cerebral cortex if almost completely made up of small cells 

 which are very poor in protoplasm ; some, almost reduced to their nuclei, 

 form a considerable aggregation — the anterior ganglionic mass — in each 

 half of the brain. The cephalic ganglion corresponds to the " proto- 

 cerebrim] " and " deutocerebrum" of Insects, but forms a very homo- 

 geneous whole. The author gives the name of optic lobe to a ganglionic 

 region which, contrary to the description by Carriere of P. edwardsi, 

 exists behind the retina. There is no true optic nerve, but a short 

 pedicle of dotted substance traverses the cerebral cortex and passes at once 

 into the eye. The two symmetrical regions whence the optic pedicles arise 

 are connected by a commissure. The anterior medullary mass is large, 

 ovoid, and formed of dotted substance ; it sends forward into the anterior 

 ganglionic mass some large ramifications, which divide there and receive 

 the continuations of the small cells. The medullary mass appears to be 

 connected with its homologue of the opposite side by a small commis- 

 sural cord. The whole system reminds the author of the pedunculated 

 body of Insects ; there is a dorsal pad which resembles in its structure 

 the stratified organ of the Araneida. The olfactory lobe is characterized 

 by the presence of numerous spherical or ovoid olfactory glomeruli. 

 The enigmatic appendage on the ventral surface of the brain is not 

 stalked ; its essential elements are elongated cells which differ from the 

 nerve-cells, and bound an excentric lenticular space which is occupied by 

 a mass of chitinous substance. There are no nerve-fibres, but elongated 

 cells, which are probably destined to facilitate the nutrition of the organ, 

 penetrate into the cerebral cortex. 



S. Arachnida. 



Malpighian Tubes and " Hepatic Cells " of Araneina.* — Dr. A. B. 

 Griffiths and Mr. A. Johnstone have examined the Malpighian tubes and 

 hepatic cells of Tegenaria domestica ; the secretion of the former was 

 found to yield uric acid, which was found in combination with sodium ; 

 no urea, guanin, or calcium phosphate could be detected in the secretion. 

 The chemical tests applied to the secretion of the so-called liver show 

 that this organ in the Araneina is similar in its functions to the pancreas 

 of the Vertebrata. 



Anatomy of Atax ypsilophorus and A. Bonzi.f— Dr. P. Girod has 

 examined the anatomy of these Hydrachnids, parasitic in Anodonta and 

 Unio. There are three pairs of buccal glands ; into the stomach there open 

 two large lateral caeca and one larger superior or cephalic caecum. The 

 excretory organ lies dorsally to the stomach and is Y-shaped ; there is 

 no terminal intestine, and no anus ; nor is there a cloaca common to 

 the rectum and the excretory organ ; the latter opens by a special pore. 



In the dorsal wall of the pharynx there are large rounded cells, 

 glandular in appearance ; the independent buccal glands are formed of 

 a delicate tunica propria and a single row of large cylindrical cells ; the 

 protoplasm of these is homogeneous, and the nucleus is well marked. 

 The walls of the stomach and caeca are lined by a single layer of cells, 

 some of which are parietal and some secretory: the former contain 



* Proc. E. Soc. Edinb., xv. (1887-8) pp. 111-4. 

 t Bull. Soc. Zool. France, xiv. (1889) pp. 107-10. 



