566 SUMMARY OF CURRENT RE8E.VRCHES RELATING TO 



sents a fresh-water Mytilus, and a form that closely resembles the oyster 

 can be traced throiigh ^thcria to Muelleria. 



In another direction the author traces development from the central 

 Area types to the extreme of Aspergillum. In this procedure, Lucina, 

 CardUuii, Venus, Mya, Solen, Macha, Teredo, Gastrochsena, and Clavajella, 

 are discussed. 



In the first branch towards Ostrea, the fulcrum moves from a position 

 between the two equally largo adductors, toward the oral pole of the 

 body. This brought the anterior adductor in a line with the fulcrum 

 and posterior adductor, where, being of no use, it disapixjared. In the 

 other direction, development is in the antero-posterior direction, the 

 shell, however, not taking part in the growth until a form is reached 

 where the shell is exceedingly small and the animal protected by a sup- 

 plementary deposit of carbonate of lime. 



Crystalline Style.* — Herr B. Haseloff has made some very interest- 

 ing observations on the formation of the crystalline style in mussels. 

 Acting on the suggestion of Prof. Mobius that the structure in question 

 represented reserve food-material, the author made experiments with 

 Mytilus ediilis. The structure seems in natural conditions to be almost 

 constantly present. In some specimens, however, which were set apart 

 and starved, the style disappeared in a few days, and that the more 

 completely, the more complete the fasting. The demonstration was 

 completed, however, by re-feeding some mussels of the same set as those 

 in which the style had disappeared ; the result seemed to be the re- 

 aj^pearauce of the style. Some observations by Hazay agree with those 

 of the author, and the supposition of Prof. Mobius that the crystalline 

 style represents reserve material seems quite justified. Herr Haseloff 

 does not regard it as a secretion, but a chemical modification of surplus 

 food. 



MoUuscoida. 

 B. Polyzoa. 



Spermatogenesis in AlcyoneUa.f — Prof. A. Korotneff has studied 

 the development of the spermatozoa in Alcyonella fungosa, which seems 

 to be a particularly fit object for the investigation of spermatogenesis. 

 The main steps of the process, which exhibits the well-known stages 

 named by v. la Valette St. George, has been already summarized ; but a 

 few other results may be recorded. 



Head, neck, and tail develope independently, and are secondarily 

 united. In the sperm of Ascaris, the amoeboid portion is the much 

 shortened tail, which here is more complex than usual, and includes 

 several fibrils instead of only one. Referring to van Beneden's obser- 

 vation that the fibrils of an Ascaris sperm were cross-striped, Korotneff 

 characterizes a spermatozoon as " a free-living, highly specialized 

 muscle-cell." 



Fresh-water Polyzoa. | — Dr. K. Krapelin has monographed the fresh- 

 water Polyzoa of Germany. The part published treats of the morphology 

 and systematic. The history of research is first discussed, then the 



* Biol. Centralbl., vii. (1888) pp. 683-4. 

 t Arch. f. Mikr. Anat., xxxi. (1888) pp. 334-47 (1 pi.). 



j Ahh. Naturwiss. Hambiu-g, x. (7 pis.). Cf. Biol. Centralbl., vii. (1887) 

 pp. 724-5. 



