GOfi SUMMARY OF CURRENT RESEARCHES RELATING TO 



accentuated while the seminal tubes still remain in an embryonic condi- 

 tion, till after the sixtieth day. The explanation offered is that the 

 internal secretion of the interstitial cells serves as a stimulus for the 

 development of the secondary sex-characters. 



Teratology of Fishes.* — James F. Gemmill, in this important work, 

 has primarily dealt with the structural aspect of the major abnormalities 

 — double monstrosity, triple monstrosity, and cyclopia — occurring in 

 fishes, particularly in the trout and salmon. In addition, he discusses 

 minor abnormalities, such as those affecting skull, vertebral column, 

 fins, and coloration. The general conclusions of his valuable memoir 

 may be briefly stated. 1. Each of the recognized types of monstrosity, 

 major as well as minor, can arise in a spontaneous or autogenetic manner, 

 by abrupt germinal variation. 2. Most of the recognized teratological 

 types, and particularly the major ones, are also capable of being produced 

 by environmental factors acting during the course of development. But 

 the environmental factors have not more than a shunting action. They 

 cause the course of development to deviate along certain lines which 

 the organism or structure is capable of following. :-!. On the whole the 

 two groups (namely, those of autogenetic and of acquired abnormalities) 

 tend to coincide, but the former will be found to have a wider content. 

 The fact that a particular abnormality appears spontaneously is an 

 argument for, and not against, the prol)ability that the same abnor- 

 mality can be artificially produced. The converse proposition carries 

 with it an even stronger degree of likelihood. Teratological variation 

 is thus not essentially different from ordinary variation, but the major 

 tt-ratological variations will not, as a rule, have any influence on evolution. 



Tunicata. 



Nervous System of Salps.f — Gerhard Dober has studied this in 

 numerous species. The shape of the ganglion differs in different species 

 from oval to spherical. Its position also differs in different species ; 

 thus it is close to the ingestion opening in S. amboinensis, and near the ' 

 middle of the body in S. hexagona. The size of the ganglion increases 

 with that of the animal ; the aggregate forms have smaller ganglia, the 

 solitary forms have larger ganglia. 



Salps exhibit fibrous non-nucleated nerves. In the aggregate form 

 ■of S. assymetrica there are nuclei at the base of.the nerves. The number 

 of nerves is in proportion to size ; thus there are about twenty in S. 

 mucronata, and about seventy in the sohtary form of S. pinnata. The 

 number is greater in the solitary forms than in the aggregate forms of 

 the same species ; it varies somewhat within the species ; it is far 

 greater than in other Tunicata. Except in the aggregate form of S. 

 mnaria, the number of nerves on the two sides of the heart is unequal. 

 The number of nerves is not directly correlated with the musculature ; 

 ihus the solitary form of *S'. hexagona, which is very muscular, has 



* The Teratology of Fishes, 4to, Glasgow (1912) pp. xvii. -f 73 (26 pis.). 

 t Zeitschr. wiss. Zool., c. (1912) pp. 387-444 (1 pi. aud 45 figs.). 



