50 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of a Pterolychid whicli may be distinguislied as BdellorhyncJius poly- 

 morphus, which lives on such Anatidas as Erismatura, Querquedula, 

 and Spatula: while some of the males have the normal rostrum, 

 others have the hooklets of their mandibles disproportionately elon- 

 gated ; in form these mandibles vary greatly ; and indeed it is only 

 the hinder part of the body which is normal and identical in these 

 two sets. The genital organs are similar, but the copulatory cnpules 

 seem to be a little better developed in the normal males. Figures of 

 the forms here noticed will be published. 



5. Crustacea. 



Spermatog-enesis of Podophthalmate Crustacea.*— G. Hermann 

 finds that the testicular cells of podophthalmate Crustacea give rise 

 to spermatoblasts, each of which becomes a spermatozoon. As in the 

 Vertebrata, the formation of these commences by the appearance of 

 a " cephalic nodule " in the spermatoblast, which becomes converted 

 into a transparent vesicle, which gradually grows spherical. At the 

 anterior pole of this vesicle there soon appears a kind of outgrowth 

 of the wall which projects into the cavity ; a short time afterwards a 

 delicate rod appears at the opposite pole. These two outgrowths 

 elongate, and, uniting, form a " central column " which extends from 

 one to the other pole of the " cephalic vesicle." In the brachyurous 

 Decapoda the vesicle generally becomes bell-shaped, the nuclear sub- 

 stance forms a kind of hemispherical cap, from the edges of which 

 are emitted a number of filiform prolongations, varying in number 

 and size. In this way the so-called radiate cell is produced. The 

 body of the spermatoblastic cell seems to disappear very early. 



In most of the Macroura the cephalic vesicle elongates, and a 

 collar of opaque homogeneous substance is developed ; this is at first 

 circular, but soon becomes triangular, while the three angles are 

 drawn out into filiform rigid prolongations. The fundamental pheno- 

 mena appear to be constant, but the definitive form of the cephalic 

 vesicle varies in various species. Astacus fluviatilis resembles the 

 Brachyura by the possession of a number of prolongations. 



It is to be noted that, in consequence of a kind of gradual con- 

 densation of their substance, the adult spermatozoa are smaller in size 

 and often also simpler in structure than the transitory forms which 

 appear in the course of their development. 



It is possible that the great differences in the details of the 

 structure of spermatozoa may throw some light on the zoological 

 affinities of their possessors. 



American Isopoda.t — O. Harger has a report on the Isopoda 

 collected by the ' Blake ' ; though the number of species is small the 

 collection was interesting for the large proportion of forms either 

 new or not hitherto known from the American coast, while others 

 have been only imperfectly described. Cirolana impressa and Bocinela 

 oculata are the two new species. 



» 



* Comptes Eendus, xcvii. (1883) pp. 958-61. 



t Bull. Mils. Comp. Zool. Camb., xi. (1883) pp. 91-104 (4 pls.3. 



