ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 299 



Durinsr development the visceral mass disintegrates so that at the time 

 of hatching the mantle contains a great number of Cypris larvi» ready 

 to emerge. An apical perforation is made in the mantle, and on the 

 moult of the cuticle a way is thus opened to the exterior for the larvae. 



The escape of the larvae is contemporaneous with or Soon followed 

 by a moult of the host. The empty shells of external sacs are carried 

 away with the cast skin, and the terminal swellings of the root system 

 emerge as a new crop of external sacs. Development of the germ-cells 

 in the lacunar tissue of the roots may take place m situ as well as in the 

 external sacs, but it does not apparently proceed very far. The large 

 number of external sacs in both Thompsonia and Fdtogaster socialis 

 Kriiger (which is figured on Pagurus alaskensis) is accounted for by a 

 process of budding from a single original larva. The genus is not 

 primitive, but very specialized. The effect of the parasite upon the 

 host seemed to be negligible in the specimens examined. The genus 

 Thylacoplethus Coutiere is synonymous with Thompsonia Kossmann. 



Annulata. 



Sabellidae and TerebellidaB.* — W. C. Mcintosh discusses the British 

 Sabellidai, which number over twenty species, besides those dredged by 

 the ' Porcupine ' and the ' Knight Errant,' and by Canon Norman off 

 Norway and Finmark, and also the Sabellidas and Terebellid^ collected 

 by Dr. Whiteaves in the Gulf of St. Lawrence. His notes include 

 descriptions of a number of new and interesting forms. 



Leech on Catfish.f — W. Harold Leigh-Sharpe describes Platybdella 

 anarrhichse parasitic on the gills, the walls of the branchial chamber, 

 and the pectoral region generally of the catfish, Anarrhichas lupus. The 

 body is cylindrical, moderately depressed, without papillae or respiratory 

 vesicles, divided, though not very distinctly, into an anterior " neck " 

 and a posterior abdomen, very transparent. It does not roll itself up 

 when at rest. The oral sucker is cupuliform and of moderate size. 

 The posterior sucker is obliquely affixed and very distinct. The annuli 

 are only made out with difficulty, and the number to a typical or 

 abdominal somite is uncertain. The testes seem to be only five pairs. 

 The bursa is insignificant. Pigment cells are absent. A key to the 

 Ichthyobdellidae is given. 



Nematohelminthes. 



Structure and Position of Acuariid8B.| — L. G. Seurat discusses 

 some of the characteristics of this family of Nematodes — the two lateral 

 lips, the oesophageal papillae inserted behind the nerve ring, and the 

 tube-shaped cuticular ovijector. The relations of Acuariidae to Pilariidae, 

 Spiruridge, and Heterakidffi are dealt with. 



* Ami. Mag. Nat. Hist., xvii. (191G) pp. 1-68 (4 pis.). 

 + Parasitology, viii. (1916) pp. 274-93 (11 figs.). 

 ; Comptes Kendus, clxii. (1916) pp. 141-3. 



