560 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Spermatozoa of Eledone moschata.* — M. A. Sabatior finds a double 

 metbod of spermatogenesis in Eledone moschnta, comparable to tbat already 

 observed in some Gastropods by MM. Koebler and Robert. In one set, 

 the bead is formed by a fine, very regular spiral ; in tbc otbcr kind, tlio 

 bead, wbicb is much longer, is a simple straight or very irregular sinuous 

 filament. In the spermatoblasts wbicb give rise to the spiriform 

 spermatozoa the chromatin of the nucleus is condensed at the centre of 

 the cell into a mass which is at first globular, but soon becomes club- 

 shai^cd. The nuclear membrane becomes invisible, and the chromatic 

 rod is situated at the centre of the cell, which also becomes elongated. 

 The cytoplasm which surrounds the rod becomes very delicate, and 

 becomes largely aggregated round the thinner end of the club-shaped 

 body. The thicker end of the latter frees itself from the body of the 

 cell, and gets at its end a very fine colourless filament which appears to 

 be formed by the elongation of part of the cytoplasm ; this is the tail of 

 the spermatozoon. As the rod elongates it becomes more and more 

 delicate, till at last its massive form gives place to a spire with regular 

 turns, which are at first close, and gradually separate from one another. 



The filiform spermatozoa are developed after a different fashion. 

 The chromatin of the spermatoblasts becomes condensed at the periphery 

 of the nucleus, close to the nuclear membrane. It is at first an arc 

 which elongates as it grows. The cell becomes ovoid, and the chromatin 

 narrows at one extremity, which carries a mass of granular protoplasm. 

 The remainder remains rolled round a clear, spherical mass ; it next 

 elongates and loses its spiral form, when the spermatozoon appears as a 

 chromatic filament with a very long tail, and attached by its base to a 

 mass of granular cytojjlasm, which, in its turn, disappears. 



M. Sabatier's observations on Eledone have confirmed him in the 

 opinion he long since exi)re8sed that the vermiform spermatozoa of 

 Paludina are true colonies of spermatozoa, corresponding to a group of 

 spermatozoa, the heads of which have become fused, while the tails have 

 remained distinct. 



B. Pteropoda. 

 Musculature of Heteropoda and Pteropoda.|— Herr G. Kalide has 

 investigated the musculature of the Heteropoda and Pteropoda with the 

 view of throwing light on the morphology of the foot of Mollusca. In 

 the former the nmsculature of the trunk consists of two muscular strata 

 lying one above the other ; the fibres of the upper layer pass from above 

 forwards to below backwards, and those of the lower layer from below 

 forwards to above backwards. In the caudal region, the visceral sac, 

 and the proboscis, this musculature has a longitudinal direction. Above 

 it there is a cii'cular muscle which covers the greater part of the body 

 (^Carinaria), or is limited to the proboscis {Pterotrachea). The fin has 

 its own musculature, which is connected with the spindle-muscle. The 

 author thinks that sufficient attention has not been given to the fact that 

 the musculature of the fin has no connection with that of the trunk, 

 while that of the anterior processes of the body passes continuously into 

 the trunk. If the fin of the Heteropoda be homologous with any part 

 of the body of any other Mollusc, that part must have a similar arrange- 



* Comptes Kendus, cvi. (1888) pp. 954-6. 



t Zeitschr. f. Wise. Zool., xlvi. (1«88) pp. 337-77. 



