ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 673 



tain much yolk, segmentation is total and unequal, and the gastrula is 

 epibolic. Till the fifteenth day the larvae show strong positive photo- 

 taxis, at the end of the fifteenth day they lose their cilia and sink to 

 the bottom. The larva is telotrochal and possesses large ectodermal 

 cephalic glands. 



Nephridia of Polychaeta.*— Mr. E. S. Goodrich, in Part III. of his 

 memoir on this subject, discusses the anatomy of the nephridia in the 

 Phyllodocidae, the Syllida?, and the AmphinomidaB, together with some 

 other forms, summarises the anatomical results contained in Parts L, 

 II., and III., and upon the basis of this work, draws the following 

 conclusions in regard to the homology of the Polychaete nephridium, 

 and its relation to the genital funnel. In the first place he opposes 

 the view that the genital funnel is merely a specialised portion of the 

 nephridium, and contends that its development shows it to be the 

 homologue of the genital ducts of other Annelida. His results show 

 that in the Phyllodocidge the nephridia have no internal openings, but in 

 most segments a genital funnel fuses! with the nephridium at maturity, 

 the compound organ forming the genital duct. In some other families 

 (Nereidae, Nephthyidre, &c.) various conditions of the genital funnel 

 occur, showing more or less intimate relation between nephridium and 

 genital funnel. This culminates in the Hesionid Irma, where the 

 fusion is so complete that the two organs can only be histologically 

 distinguished. In the remaining large families (Eunicidae, Amphi- 

 nomidae, <frc.) the condition occurs which has been always regarded as 

 the typical one for Polychastes — that is, there is a" nephridium " with 

 a large trumpet-shaped internal opening, which also functions as a 

 genital duct. The author believes, however, that this " nephridium " 

 is in reality produced by the complete fusion of true nephridium and 

 genital funnel. In consequence, he believes that three main types of 

 nephridia occur in Polychaeta : — (1) those found for example in Alciope, 

 which are blind internally and are furnished with solenocytes ; these are 

 probably primitive and homologous with the protonephridia and flame- 

 cells ( = solenocytes) of Nemertines ; (2) the Nereid type, where there 

 is a true nephrostome, may be supposed to have arisen from the above 

 by the development of the internal opening ; (3) the most specialised 

 type, exemplified in Polymnia, is the nephromixium, produced by the 

 union of true nephridium and genital funnel. This is the type most 

 commonly found in Polychaeta. The author believes that the variations 

 in the nephridia in Polychsetes might be readily utilised as a basis for 

 a revised classification, and that the adoption of the above conclusions 

 brings the group, in regard to the excretory organs, more into line 

 with the Oligochaetes and Hirudinea, and diminishes the difficulties in 

 deriving these from the excretory system of Nemertines and Platy hel- 

 minths, in which tbe excretory ducts are distinct from the genital. 



Heart-body of Oligochsetes.f— Dr. M. de Bock finds that this body 

 exists in Lumbriculus, Bhynchelmis, Tubifex, and Nais, as well as in the 

 Enchytraeidaa, and that it is made up of metamorphosed amcebocytes 



* Quart. Journ. Micr. Sci., xliii. (lf>00) pp. 699-748 (6 pis.). Cf. this Journal, 

 1897, p. 384 ; 1899, p. 36. 



t Rev. Suisse Zool., viii. (1900) pp. 107-66 (2 pis.). 



