702 SCIENTIFIC RECORD FOR 1883. 



deep-sea fauna the fauna of darkness." Professor Fuchs goes so far as 

 to contend that " the occurrence of the deep-sea fauna is in no way con- 

 nected with the temperature of water." 



The views thus enumerated by Professor Fuchs will not go unchal- 

 lenged, and indeed all his propositions appear to be too much general- 

 ized at least, and are more or less contradicted by facts within our 

 knowledge. 



The origin of sexual differences. — The search for the cause which de- 

 termines that the offspring should be of the male or female sex has been 

 long carried on by various persons, and every now and then the discov- 

 ery of the cause is announced. Hitherto the results of investigation 

 have been illusive and unsatisfactory. Prof. E. Pfluger has recently 

 renewed inquiries into the fascinating subject, and published the re- 

 sults in the Archiv fur Physiologie (vol. xxix). His researches were 

 made on frogs, of which many hundreds were experimented upon. 



Dr. Pfluger especially investigated the question whether the concen- 

 tration of the spermatic fluid influences the sex of the offspring. Tak- 

 ing all due precautions (for the eggs are very delicate), he secured in a 

 watch-glass the spermatic fluid of the male, taken in the act of sexual 

 congress, and subjected it to various degrees of dilution in water in 

 various glasses. Eggs taken from the right uterus of the female were 

 allowed to glide into these mixtures. The experiments established two 

 facts : (1) the fertilizing power of the spermatic fluid was not diminished 

 by dilution, and " all the ova were fertilized in each observation"; (2) 

 u dilution of the male fluid had no effect on the sex of the frogs which 

 came to maturity after the artificial fertilization." 



There are three categories as to sex manifested in young frogs : (1) 

 male, (2) female, and (3) hermaphrodite. " The hermaphrodites become 

 finally either male or female, but in their earlier stages they have the 

 sexual organs of the female only ; in those which are finally to become 

 males the testicles gradually develop around the ovaries and the latter 

 are resorbed." The apparent numerical preponderance of the female 

 believed to exist in the earlier life history of the frog is illusive, and has 

 led some investigators astray, it is urged. The fertilizing power of 

 the male spermatic fluid diminishes rapidly after the end of the sexual 

 season. 



Dr. Pfluger has to think that it is " impossible" to produce offspring by 

 the union of the sexes of different species of Batrachians. Segmenta- 

 tion may commence, but this segmentation was frequently of an ab- 

 normal type. (Am. Naturalist, vol. xvn, pp. 441, 442.) 



Sense of direction in animals. — That wonderful faculty developed in 

 so many animals of being able to find their way to a long-distant spot 

 has been the subject of much speculation aud some serious investiga- 

 tions. Some of the hypotheses respecting the " sense of direction " thus 

 manifested are more ingenious than probable. A French searcher for 



