290 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



1. Dichotriaenes. Cladomes of the larger lie in the dermal mem- 

 brane. Rhabdome 2.7 mm. by 40-50 [x; protoclad 90-120 \i long; 

 deuteroclads 200-220 \i long, reaching in some specimens 300 jx. 



Lendenfeld (1906, p. 288) finds that internal to the subdermal 

 spaces lies a second layer of dichotriaenes. This is so in my speci- 

 mens. The facts further indicate that the dichotriaene begins deep 

 in the choanosome as a protriaene, that it grows and differentiates 

 as it passes toward the surface. The facts are as follows: 



The dichotriaenes beneath the subdermal cavities are smaller than 

 those of the outer layer. The difference especially concerns the 

 deuteroclads, which are about 150 \l long. Internal to these are still 

 other and smaller, obviously developing, dichotriaenes with deutero- 

 clads, which vary in length, but which are all short and, indeed, in 

 many cases minute. I give measurements of two spicules: 



Iihabdome. 

 1300 by 18 (i. 

 1000 by 16 /i. 



Protoclad. 

 90 n long. 

 100 n long. 



Deuteroclads. 

 30 n long. 

 5 m long. 



Khabdome. Claris. 



500 by 7 n 44 m long 



450 by 7 m 40 m long 



320 by 10 n 40 ft long 



300 by 7 m 32 m long 



Internal to these, and still smaller, are protriaenes, which vary in 

 size down to quite small spicules. The clads of the protriaenes rep- 

 resent, I believe, the protoclads of the later (dichotriaene) stage. I 

 give the following measurements for the protriaenes : 



Rhabdome. Clads. 



1,000 by 14 m 120 /* long. 



800 by 14 m 100 m long. 



900 by 14 fx. SO m long. 



600 by 14 n 70ittlong. 



600 by 14 m 56 m long. 



From the measurements given above it will be seen that there is 

 a very complete transitional series, ranging from the small deep- 

 lying protriaenes to the well-developed dichotriaenes. It is thus 

 fairly certain that the former are only stages in the development 

 of the latter. 



2. Anatriaenes. Cladome about hemispherical. Rhabdome 2200 

 b} r 24 [x; clads 75-120 \i. long, and stout. They accompany the di- 

 chotriaenes. Some of them pass out quite to the surface, their 

 cladomes lying external to those of the dermal dichotriaenes. Quite 

 small anatriaenes with Very Hat. shallow cladomes. lie intermingled 

 with the developing dichotriaenes (see above). These doubtless are 

 stages in development. 



A detailed examination would probably show that the cladomes of 

 the anatriaenes are well stamped with the "geographical mark*' — 

 that is. that in respect to this point, a quantitative one. the difference 

 beween specimens from different localities is easily perceived. For 

 instance, in a specimen from 1)5158 the cladomes were shallower 

 than hemispherical, about umbrella-shaped, with clads 75 \i long. 



