ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 301 



Annulata. 



Nervous System of Owenia and Myriochele.* — W. C. M'Intosh 

 gives an account of the minute structure of the nervous system as seen 

 in sections. The main feature is the partial differentiation of the nerve- 

 tissue from the hypoderm with which it is in continuity at its centre. 

 No sheath is evident anywhere, even in the mo?t distinctly outlined 

 nerve-cords posteriorly. Yet the position of the cephalic centre and its 

 connexion by two trunks with the rentral nerve-cord agree with the 

 general type. The innervation of the alimentary canal seems to be 

 carried out on a similar plan to that of the main system, viz. by contact 

 with a sensitive layer rather than by special twigs. The whole nervous 

 system, in fact, is in a somewhat elementary or larval condition. 



Calliobdella nodulifera Malm.f — W. Harold Leigh-Sharpe describes 

 this marine leech from the saithe {Gadus carbonarius) and compares it 

 with other species. The epidermis consists of a layer of columnar cells 

 elongated in a direction at right angles to the long axis of the body, 

 having their nuclei, which are large, away from the external border 

 where a cuticle is secreted. At frequent intervals among the epithelial 

 cells are flask -shaped glandular cells making mucus. The dermis is 

 rich in large flattened cells with large flattened nuclei, embedded in a 

 connective tissue matrix with numerous fibre-forming cells. The 

 dermis also includes large pigment cells. Below the dermis lie the 

 muscle layers, and below these the cocoon-gland cells. The body cavity 

 is represented by dorsal, ventral, lateral, and intestinal sinuses. The 

 ventral blood-vessel is outside the ventral sinus, one of the characters 

 distinguishing C. nodulifera from C. lophii. 



Nematohelminthes. 



Development of Ascaris.| — F. H. Stewart has studied the develop- 

 ment of Ascaris himbricoides and A. suilla in the rat and mouse. The 

 eggs hatch in the gut ; a certain number of the larvse escape iu the 

 faeces ; they can survive for at least three days, but probably succumb 

 ultimately ; the majority enter the body. The time elapsing between 

 infection and the entrance of the larvse into the body is probably not 

 more than two days. Larvse are found in lungs, liver, and other parts. 

 The diameter of a larva is three times that of a red blood corpuscle of 

 the mouse, so the larva3 cannot pass through the lumen of an ordinary 

 capillary vessel. There must be some boring. The possible routes by 

 mesenteric venules and bile-ducts are discussed. During their residence 

 in mouse or rat the larva3 grow from a length of ' 22 mm. to 1 • 4 mm. 



* Ann. Mag. Nat. Hist., xix. (1917) pp. 233-65 (6 pis.). 



t Proc. Roy. Phys. Soc. Edinburgh, xx. (1917) pp. 118-22 (2 pis. and 1 fig.). 



X Parasitology, ix. (1917) pp. 213-27 (1 pi. and 9 figs.). 



