ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 175 



Convoluta flavibacillum, which has not been previously noticed from 

 this locality. About forty were found in a collection of C. roscoffensis, 

 and the peculiar fact was observed that on the ventral surface of each of 

 them there was a young C. roscoffensis, clinging on by its dorsal surface. 

 When they were separated in an aquarium, they were re-united in half 

 an hour. The one species has chlorophyll, the other has not. But the 

 meaning of the association is quite obscure. 



Incertae Sedis. 



Nervous System of Cristatella mucedo.* — A. Gerwertzhagen de- 

 scribes the central nervous system, the innervation of tentacles, the 

 epistomal and oral nerve-rings, the sensory cells of the tentacle-crown, 

 the innervation of epistome and tentacular sheath, the colonial nervous 

 system, and the sympathetic system. The so-called oesophageal ring of 

 Gymnolaemata is homologous with the oral nerve-ring of Cristatella ; the 

 ganglion of Cristatella is probably supra-cesophageal, but the definite 

 developmental proof of this is lacking. The author compares the 

 nervous system of Cristatella with that of Phoronis, Brachiopods, 

 Chaetognaths, and Pterobranchia, but does not discover any close 

 affinities. 



Echinoderma. 



Echinoderm Hybridization. f— David H. Tennant calls attention 

 to the apparent confusion that exists among observations on hybrid 

 Echinoid larvae, as to whether plutei of a maternal type, a paternal 

 type, or of mixed form are derived from certain crosses. Different 

 results have been obtained by different investigators, and by the same 

 investigators working in different regions, or in the same region in 

 different seasons. He points out that the results differ according to 

 the conditions. Under some conditions we may obtain larvae of a 

 maternal type with respect to certain characters ; under other conditions 

 larvse of a paternal type ; and under still other conditions larvae of a 

 blended type. The real problem in Echinoderm hybridization is the 

 determination of the conditions under which these different types appear. 

 Another point to which Tennant directs attention is the importance of 

 determining the extent and nature of the variations in the skeleton 

 before using skeletal characters as indices of inheritance in crosses. 

 Moreover, in proper material, parental influence may be demonstrated 

 in stages even younger than the pluteus. In fertilizations of Cidaris 

 ova with sperms of Toxopneustes or of Hipponoe, the influence of the 

 foreign sperm was clearly seen, in the early gastrula stage, in the changed 

 site and earlier appearance of the primary mesenchyme. 



* Zeitschr. wiss. Zool., cvii. (1913) pp. 309-45 (3 pis. and 3 figs.), 

 t Science, xxxvii. (1913) pp. 535-7. 



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