172 



men among those kept in the same dish discharging its sperm at the same 

 time. The eggs were few in number, amounting only to ca. 90; the specimen, 

 however, still contained some more, so that, evidently, not all the eggs 

 are discharged at the same time, as is the case in Ophiothrix angulatus, 

 in which they are all discharged at one time, almost as by an explosion. 

 — The specimen was not observed to assume a special attitude while dis- 

 charging its eggs, such as is the case in Ophioderma brevispina, according 

 to the observations of Grave. 



Owing to the small number of eggs the material was insufficient for a 

 complete study of the details of the interior changes during the meta- 

 morphosis, a study which would have been of the greatest interest for a 

 comparison with the results obtained by Caswell Grave i) in Ophioderma 

 brevispina. Although I tried many times to get another culture, I did not 

 succeed, so I had to make a very careful use of the httle material avail- 

 able and to preserve no more specimens of the different stages than 

 strictly necessary. 



The size of the eggs is 0.2 mm ; they are red coloured. They were lying 

 free at the bottom, not floating at the surface, as did those of 0. brevispina. 

 The cleavage is regular and total. In the course of 15 hours the embryos 

 were found to be in the gastrula stage, pearshaped, of a beautiful pink 

 colour, especially towards the pointed anterior extremity ; they were swim- 

 ming close to the bottom. In the course of ca. 24 hours it became evident 

 that the larva would turn out to be of the vermiform type, like that of 

 0. brevispina, as described by Grave. At that age the embryo has an 

 elongate, triangular shape, with a narrowing below the anterior end, which 

 thus becomes like a rounded knob (PI. XXXI, Fig. 6). It is ciliated all 

 over, without any ciliated bands as yet ; what looks like a transverse band 

 in the figure quoted is not really one ; it is due to the fact that a transverse 

 fold is formed in the posterior end of the body, on the ventral side, the 

 apparent band being only the edge of the lobe. In this fold the gastrula 

 mouth lies which is thus no longer in the posterior edge of the embryo; 

 it appears to be closed already at this stage. The embryo keeps swimming 

 close to the bottom as in its youngest stages. 



PI. XXXI, Fig. 5 represents a frontal section of a larva 26 hours old. 

 It shows a double sac at the upper end of the archenteron, apparently 

 still in connection with the latter — but the histological preservation is 

 not sufficiently good to allow the definite ascertaining of this question. 

 The larger of these sacs doubtlessly represents the hydrocoel, while the 

 smaller apparently is the anterior right enterocoel. In the posterior end two 



') Caswell Grave. Ophiura brevispina. Mem. Nat. Acad, of Sc. VIII. Baltimore 1900. 

 (Mem. Biol. Lab. Johns Hopkins Univ. 4). 



