304 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Development of the Gill in Mytilus.* — E. L. Rice gives a pre- 

 liminary abstract of inquiries on this subject. He notes specially an 

 interesting parallel in the development of the inter lamellar connections. 

 This connection in its finished form is a simple bar containing a blood 

 channel, and connecting the two branches of one and the same filament. 

 In an early stage the two branches are connected by a continuous plate 

 of tissue extending from the bend of the filament upwards for a short 

 distance. This is the adult condition in Area, and Modiola. Later a 

 perforation appears in the plate, and the portion above the perforation 

 is transformed into the characteristic bar-like connection. 



Orientation of Tridachnids within their Shells.f — Anthony 

 corroborates the observations of Lacaze-Duthiers which showed that 

 there is not, as is often asserted, any torsion of Tridacna and Hippopus 

 within their shells. There has been a remarkable shortening of the 

 antero-posterior axis and an elongation of the dorso-ventral and trans- 

 verse axes, in adaptation, probably, to the mode of life and the massive- 

 ness of the shells. 



Arthropoda. 



Excretion in Arthropods.} — L. Bruntz gives an account of the 

 excretory apparatus in Arthropoda, of which he has examined a very 

 representative series. Of kidneys opening directly to the exterior there 

 exist antennary, maxillary, labial, podal, and coxal forms. These are 

 organs consisting of two essential parts, a sacculus or terminal vesicle 

 with epithelium, whose cells have the property of eliminating ammo- 

 nium carminate injected into the coelome, and a labyrinth bringing 

 the sacculus into communication with the exterior. In the majority 

 the labyrinth was proved functional by its elimination of injected 

 indigo-carmine. Excretory organs opening by the intermediary of the 

 digestive tubes are Malphigian tubes, cseca of mid-gut and liver. The 

 liver tubes of all higher Crustacea were found to eliminate aniline 

 colours. A third type is the closed organ which accumulates or trans- 

 forms the waste products. This is represented (1) by the nephrocytes. 

 These are variable in form, groups of cells consisting of fibrillar or 

 vacuolar cytoplasm containing masses of excretory products, upon which 

 carminate may be deposited, or it may appear as granules in the cyto- 

 plasm. 



Generally in one species, there is one kind of nephrocyte, which 

 may be isolated, or grouped into a dense tissue. They are always on 

 the track of the blood currents, they may be ventral or dorsal, in the 

 head (Amphipods), cephalothorax (Arachnids), thorax (Copepods), or 

 on various situations on the appendages. The third type of excretory 

 organ — the closed organ — is also represented (2) by the uric cells of 

 the fatty bodies. These eliminate vesuvin around the granules of 

 sodium urate. 



* Ohio Naturalist, iv. (1904) p. 51. 



+ Comptes Kendus, exxxviii. (1904) pp. 296-8 (2 figs.). 



% Arch, de Biol., xx. (1903) pp. 217-422 (3 pis.). 



