586 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the tulip-root discfisc of oats, in which he fouufl in specimens supplied 

 by Miss Unuerocl the constant presence of I'ljlenchtis devasiatrix. 



In his final report * the author treats of other diseases of onion, 

 hyacinth, clover, fuller's teasel (Dipsaciis) &c., and gives in all nine 

 fii'ures of affected plants. The details have rather an agricultural than 

 a general biological interest, though the latter is by no means over- 

 looked. 



y. Platyhelminthes. 



Embryogeny of Fresh-water Dendroccela.f — Dr. P. Hallez has 

 observed that in Plcmaria pohjcliroa the cocoon is formed in the uterus 

 and not in the genital cloaca, as is the case in Dendrocoelum lacteum ; 

 he believes that the bursa copulatrix will be shown to be a propelling 

 organ, the function of which is to introduce the ova and fertilizing ele- 

 ments into the uterus. An account is given of the yolk-cells, their 

 structure, and the formation from them of a syncytial mass which 

 surrounds the eggs. The period of maturation of the egg is character- 

 ized by the formation of a certain number of clear vesicles (three in the 

 case of D. ladeum) which arise at one of the poles of the egg, in the 

 neighbourhood of the nucleus. These bodies are, finally, eliminated ; 

 they are certainly homologues of the formations to which Sabatier has 

 especially called attention ; the author suggests that they have no more 

 significance than the liquid which is exi^elled by the contractile vesi- 

 cles of the Protozoa. No polar globule is formed. The fecundated 

 egg is surrounded by a score of radial vitelline cells, which are nearly 

 conical in form, and are attached to the egg by their base. The blasto- 

 meres of the 2-stage are equal, as are also those of the 4-stage. After 

 the 8-stage the surrounding syncytium begins to be formed. About tho 

 stage in which there are 20 cells a new series of vitelline cells becomes 

 disposed radially around the embryo, and this likewise becomes syn- 

 cytial. From this mode of distribution of the nutrient elements M. 

 Hallez applies the term ectolecithal to the eggs of fresh-water Dendro- 

 coela. 



The first organ to be diffierentiated is the primitive ectoderm ; this 

 is formed by the most external embryonic cells, which approach the 

 periphery of the syncytium, and there become flattened. During the 

 whole course of development fresh embryonic cells are continually 

 becoming flattened on the sui-face of the embryo, and being converted 

 into ectodermic cells ; in this way the ectodermal membrane of the 

 embryo insensibly passes into the epidermic investment of the adult. 

 When the primitive ectoderm has been formed, three groups of blasto- 

 meres may be distinguished in the embryo ; those of the rudiment of 

 the pharynx consist of about twenty cells ; immediately behind these 

 there are four primitive endodermic cells ; and, lastly, there are about 

 fifty migratory cells. Till the provisional pharynx begins to function, 

 the archenteron is merely lined by the four initial cells of the endoderm ; 

 but when the vitelline cells pass into the intestinal cavity, the endoderm 

 increases considerably in size, and some of the migratory cells become 

 connected with the four primitive endodermic. The blastomeres, when 

 undergoing histological differentiation, incorporate a certain quantity of 

 the nutrient syncytium which surrounds them. After the embryonic 



* Biol. Ceiitialbl., viii. (1SS8) pp. 1G4-78. 



t Arch. Zool. Expc'r. et Gen., v. (18«8) pp. xxxix.-xliii. 



