582 SUMMARY OF CURRENT RESEARCHES l.'KLATING TO 



North American Larval Trematodes.* — \V. \V. Cort describes a 

 large aumber of cercarise, of Monostome, Amphistome, Distome, Eclii- 

 nostome, Microcercous, Furcocercous, Polyadenous, Ornate, and Micro- 

 cotylous types. He distinguishes characters which foreshadow those of 

 the adults and those peculiar to the larval existence. The classifications 

 proposed by Liihe and Lebour are discussed. 



Echinoderina. 



Artificial Parthenogenesis of Sea-urchin Ova.f — A. P. Dustin has 

 made a slight modification of Delage's method of inducing partheno- 

 genetic development in sea-urchin ova. Delage added to 300 c.cm. of 

 sea-water, 700 c.cm. of an isotonic solution of saccharose, 15 centigrams 

 of tannin dissolved in distilled water, 3 c.cm. of normal ammoniacal 

 solution. The ova were left for an hour in the mixture, then washed 

 several times, and then placed in sea-water. Some hours later the first 

 cleavages appeared. 



Dustin diluted the mixture with an equal volume of sea-water, or 

 with twice as much, and found that the first asters appeared in 1 hour 

 or lj hours, while the eggs were still in the diluted mixture. Very good 

 results were also obtained by adding to Delage's mixture an equal 

 volume of saccharose solution (388 per 1000), or twice as much. When 

 the ova were replaced in sea-water they soon developed into larva?. 



Activation of Sea-urchin Ova.$ — A. Brachet has made a num- 

 ber of experiments on the ova of Paracmtrotus lividus, treated for two 

 minutes with butyric acid, after Loeb's method. 1. Some eggs after 

 treatment were placed in sea-water containing spermatozoa ; 60 to 70 p.c. 

 formed a membrane, were fertilized, and developed into plutei. 2. 

 Others, placed in pure sea- water, formed a typical fertilization membrane 

 in less than two minutes. After ten minutes spermatozoa were added. 

 In not more than 1 p.c. did a spermatozoon enter and induce segmenta- 

 tion. The others underwent the cytolysis characteristic of the action of 

 butyric acid. 3. Another set of eggs placed in pure sea-water formed a 

 membrane within twenty minutes. Spermatozoa were then added. As 

 in the first set, 60 to 70 p.c. were fertilized and proceeded to develop. 

 4 and 5. In two other sets the eggs were kept thirty to forty minutes in 

 the pure sea-water before spermatozoa were added. As in the second set, 

 only about 1 p.c. were fertilized and proceeded to develop. 6. In an- 

 other set the eggs remained fifty minutes in the pure sea-water. 

 Almost all had then formed a membrane, and radiations had appeared 

 around the nucleus. Nevertheless, after the' addition of spermatozoa 

 60 to 70 p.c. were fertilized and proceeded to develop, as in sets 1 and 3. 

 The same result followed when the ova were left for seventy minutes in 

 the water. 



The following conclusions are drawn. The fertilization membrane 

 and the perivitelline fluid which accumulates beneath it do not form a 



* Univ. Illinois Bull., xii. (1915) No. 45, pp. 1-86 (8 pis.). 

 t Comptes Eendus, clxi. (1915) pp. 356-9. 

 t Comptes Rendus, clxi. (1915) pp. 359-61. 



