664 SUMMARY OF CURRENT RESEARCHES RELATING TO 



5. Lamellibranchiata. 



Structure of the Heart in Bivales.* — P. Lozinski has studied this 

 in Anodonta, Unio, Ostrea, Lima, Venus, Tapes, and Pecten, and finds 

 that there are always three distinct layers, which are described in detail : 

 (1) a single-layer of pericardial epithelium ; (2) a connective-tissue layer 

 with isolated muscle-spindles, running parallel to the pericardial epithe- 

 lium ; and (3) the proper heart musculature, with bundles crossing one 

 another in all directions. There is no cardiac endothelium. 



Minute Structure of Visceral Ganglion of Anodonta.t — T. Frieden- 

 felt describes in detail the course of the fibres in this ganglion, the 

 fibres of the posterior pallial nerve, the commissure in the ganglion, 

 the fibres of the cerebral connective, and the various forms of cells. 



Pericardial Glands of Bivalves.} — Henriette Boltzmann describes 

 these in Gyprina, Mya, Astarte, and Sphcerium, and corroborates Clrobben's 

 results. The pericardial gland is a specially differentiated part of the 

 ccelomic epithelium of the pericardium, on the one hand above the auricles, 

 on the other hand between the two mantle lamella?. The tubules found 

 in the second position open into the pericardium. The glandular dif- 

 ferentiation may occur in either position or in both. The function is 

 excretory, and closely resembles that of a kidney. 



Arthropoda. 



Segmentation and Phylogeny of Arthropods. §— G. H. Carpenter 

 seeks to establish an exact numerical correspondence in segmentation 

 between typical Crustacea, Insecta, and Arachnida. He argues from this 

 that the Arthropods are monophyletic. 



According to Carpenter, the most primitive Crustacea were noino- 

 meristic, and the ancestors of insects and their allies must be sought 

 far down the Crustacean stem. All the Tracheata are closely allied. It 

 is shown that Polyxmus — an undoubted Diplopod — closely resembles 

 the lowest insects and the Symphyla in the structure of its mouth-parts. 

 The Malacopoda (Peripatidae) occupy an isolated position, and Insects 

 and Centipedes are much more nearly related to Crustaceans than to 

 Peripatids. The Arachnida arose from the base of the Trilobitan branch 

 rather than from the main Crustacean stem. Arthropods and Polychasts 

 represent specialised collateral branches from a common stock of micro- 

 scopic ancestors, unsegmented or with few segments between a broad 

 head-lobe and a narrow tail-somite. 



o. Insecta. 



Degeneration of Muscles of Flight in Ants after Nuptial Flight. || 

 Charles Janet notes that the relatively enormous musculature of flight, 

 which functions only once in a life-time, disappears completely after the 

 nuptial flight, and is replaced by columns of adipocytes. 



* Bull. Internal;. Acad. Sci. Cracovie, No. 1 (1905) pp. 48-62 (1 pi.). 

 t Acta Univ. Lund, xl. (1905, received 1906) pp. 1-28 (4 pis.). 

 % Arbeit. Zool. Inst. Univ. Wien, xvi. (1906) pp. 313-24 (1 pi.). 

 § Quart. Journ. Micr. Sci., xlix. (1905) pp. 469-91 (1 pi.). 

 || Comptes Rendus, cxlii. (1906) pp. 1095-7 (2 figs.). 



