.244 



NATURAL SCIENCE. 



October, 



begins to cease. In 4, t^ begins to grow. In 5, t.^ has further 

 widened itself. In section 6, the budding individual k^ has produced 

 three new individuals, which have not yet had time to become large 

 enough to press their own walls against those of the mother animal. 

 The new individuals are : one unnamed theca, which ought to be 

 denoted by f 3 ; one gonangium, ^2! and one budding individual, k^. 

 In all Dendroidea the individual is always formed in this manner. 



In section 7 the new individuals ^g, A'., and g.2 have pressed 

 their walls against those of the mother animal, so that the whole 

 section has become as it were a reflection of section i. Moreover, 

 in section 7 just as in section i the individuals have begun to 



Ss- 



Fig. 16. — Series of Transverse Sections of Didyonema rarum. 

 For explanation of lettering, see text. 



be shoved apart in order to let the gonangium gi pass over to the left 

 side. This separation is increased in sections 8 and g ; and finally 

 gi opens in section 10, which is the reflection of section 2. 



In^Didyonema rarum the gonangium is situated on the one side, 

 and^opens directly outward on the opposite side of the branch. In 

 Dendrograptus{?)bottnictis,\Nima.n, which, as regards its internal structure 

 otherwise differs little from Didyonema ranim, the gonangium also opens 

 directly outward, but on the same side of the branch as that on which 

 it is^ formed. 



In[Dictyonema peltatum, Wiman, the gonangium also opens on the 

 side on which it has grown, not, however, immediately outward, but 

 in or almost together with the theca, next to which it is situated. The 

 same is the case in Dendrograptus (?) celandicus, Wiman, and Dendrograp- 

 ticus (?) balticus, Wiman. 



In Didyonema peltatum I have had an opportunity of noticing an 

 occurrence which may be quite common in the Dendroidea, although 

 in consequence of the nature of the material it cannot very often be 



