38 



SIDONOPS ANGULATA. 



11.7 km. (6.3 miles), drift S. 73° W.; depth 53 m. (29 f.); it grew on a bottom 

 of fine yellow sand and coralline rock. The specimen of var. orthotriaena was 

 trawled at Station 2945 on February 6, 1889, in 34° N., 119° 29' 30" W., depth 

 55 m. (30 f.); it grew on a pebbly bottom. 



The similarity of the rather peculiar smooth oxyasters and oxysphaerasters 

 and the smallness of the differences of most of the other skeletal elements and 

 the soft parts of these sponges show that they are nearly related to one another, 

 a conclusion which is corroborated by the fact that they all come from the same 

 region. The differences between the two specimens from Station 2975 are so 

 slight that I do not hesitate to place them in the same systematic unit. Several 

 of the differences between these and the other two and between the latter are, 

 on the other hand, considerable. Some of these differences, as for instance the 

 much smaller size of both kinds of amphioxes in the smaller specimen from Sta- 

 tion 2945, may be due merely to differences of age or growth and are therefore 

 systematically unimportant; other differences appear to be of greater signifi- 

 cance, and of these the following may be noted: the subcortical triaenes of 

 the specimen from Station 2945 are orthotriaenes, while those of the others are 

 plagiotriaenes ; the strongylosphaerasters of the specimen from Station 4417 

 have more slender and conical rays, those of the other specimens stouter and 

 more cylindrical ones. Many of the sterrasters of the specimen from Station 

 2945 are rhomboidically distorted, while all or nearly all the sterrasters of the 

 others have regularly elliptical contours. The sterrasters of the specimen from 

 Station 2945 are slightly, those of the specimen from Station 4417 very con- 

 siderably, smaller than those of the specimens from Station 2975. The anaclades 

 of the specimen from Station 4417 are all small; in the specimen from Station 

 2945 medium sized, and in the specimens from Station 2975 large anaclades 

 occur besides the small ones. In the specimen from Station 4417 the anaclades 

 are partly triaene and partly diaene, in the two latter all the anaclades observed 

 were triaene. There can, I think, be no doubt about these differences being due 

 to congenital particularities and not to mere individual (somatic) adaptations 

 or differences of chromatin-separation or mixture before and during fertiliza- 

 tion. For this qualitative reason, and also for the quantitative reason that 

 these differences are by no means inconsiderable in extent, I think that they 

 must find systematic expression. As these variations are due mostly to pecu- 

 liarities of parts lying either, hke the strongylasters and sterrasters, close to 

 the surface, or, like the anaclades, even protruding beyond it; as structures 

 thus directly exposed to the influence of external forces are, a priori, liable to be 



