189 



Fii>. !!). Embryos of Aslerina e.iigua, in different 

 views, "/i. 



season is confined to the months March July, in the Mediterranean 

 mainly to April May). 



I shall not enter on a description of the developmental processes in A. 

 exigua; no doubt, it would be of considerable interest to see how far this 

 species agrees in this regard with A. gibbosa, but such a study would be 

 out of the scope of the present work, the more so as the discovery that 

 this species has a direct, shortened development, like .4. gibbosa, is not 

 mine. I would only call attention to the fact that the brachiolarian pro- 

 cesses are in general more 

 distinctly developed in the 

 embryos of A. exigua than 

 in those of A. gibbosa (Fig. 

 99). The sucking disk is 

 not very much developed, 

 still it is distinct enough. 



- The interpretation, first 

 set forth by Ludwig 1 ) 

 that these processes of the Asterina-embryo are homologous with the 

 Brachiolarian processes of the Aslerias-larva, is definitely proved to be 

 correct through the fact that the larva of Aslerina pectinifera passes 

 through a Brachiolaria-stage. 



In his paper "Uber die Genitalorgane der Asterina gibbosa" 2 ) Ludwig 

 mentions the fact (previously observed by Gasco) that the genital open- 

 ings of Asterina gibbosa are found on the ventral side, while in all other 

 Asteroids thus far observed they are found on the dorsal side. The fact 

 of the two species A. pectinifera and regularis having pelagic larvae raises 

 the question whether the genital openings in these species are found in 

 the same position as in .1. gibbosa or on the dorsal side, as is the rule in 

 Asteroids. It is very easily seen that there are no genital pores on the 

 ventral side in the two said species; on the dorsal side it is not easy to 

 ascertain, which of the pores seen there are genital pores, as they do not 

 differ in size from the papular pores; on following the genital ducts they 

 are however easily found, and it is thus ascertained that the genital 

 pores are really situated on the dorsal side. In A. exigua they are 

 found on the ventral side as in gibbosa. This contradicts the statement of 

 Ludwig, in the paper quoted, who maintains that in A. pentagona v. Mar- 

 tens, which is generally regarded as a synonym o'f .1. exigua, the pores 

 are found on the dorsal side. The discrepancy is probably due to Asterina 



') II. l.udwifj. Entwicklungsgeschichte der Aslerina gibbosa Forbes. Zeitschr. f. wiss. 

 Zool. Vol. '.M. 1882. (Morphologische Studien an Ediinodrrmen. II. p. 1.V1). 



*) Zeitschr. f. wiss. Zool. Vol. XXXI. (Morphol. Studien an Echinodermen. 1. p. 290). 



