ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 315 



foot with the median line unaffected by the waves, e.g. Haliotis, Trochus 

 (these forms move rapidly) ; tetrataxic, with four systems, two sets of 

 lateral alternating waves, seen in small species of Littorina. Amongst 

 the retrograde forms, both monotaxic (e.g. Chiton), and ditaxic (e.g. 

 Littorina littorea and L. rudis) occur. It is noteworthy that the retro- 

 grade forms correspond with the locomotor waves in various other 

 Invertebrate types, e.g. Oligochajtes, Nemerteans, Gephyreans, insect 

 larvas, etc. 



8. Lamellibranchiata. 



Nervous System of Razor-shell Clam.* — Gilman A. Drew has made 

 experiments with Ensis directus, which is well suited for the physio- 

 logical study of the nervous system. Continued stimulation of any 

 portion of the body has in time an effect on all the ganglia. The siphons, 

 collar, and foot may be so gently stimulated as to cause them to be with- 

 drawn without disturbing organs that receive their nerves from other 

 ganglia. The relation of the ganglia of a pair is intimate. Stimulating 

 nerves connected with one, causes organs connected with both to 

 respond promptly. Association fibres, by which ganglia communicate 

 with each other, are found only in commissures and connectives. 

 Although the anterior pallia! nerves are united, so that a connection is 

 formed between the cerebral ganglia, and the circum-pallial nerves con- 

 nect the cerebral and visceral ganglia of corresponding sides, there is no 

 evidence that the ganglia are able to communicate through them. Both 

 cerebral and visceral ganglia are provided with sensory and motor cells. 

 The pedal ganglia are apparently dependent upon the cerebral for 

 initiative. When the pedal ganglia are isolated from the others, stimu- 

 lation of the surface of the foot causes only local responses, due to the 

 direct stimulation of muscle-fibres. It would seem that the sensory 

 neurons have neither endings nor collaterals in the pedal ganglia, but are 

 continued to the cerebral ganglia. Impulses may pass in both directions 

 through any of the commissures and connectives. Stimulation may 

 cause impulses to be sent by roundabout connections when the usual 

 connections are destroyed, but the stimulation must be of considerable 

 duration, and the result is often considerably delayed. 



Distribution of Petricola pholadiformis.t — Bronishnv Debski points 

 out that C. Boettger's record of this mollusc in the German " Watten- 

 See " recpiires to be supplemented by other records of its occurrence in 

 England in 1896 and subsequently, and in Belgium in 1903. 



Arthropoda. 

 a. Insecta. 



Treatise on Insects.!— A. Berlese's treatise on insects continues to 

 appear, the latest part dealing mainly with the alimentary system, in- 

 cluding the Malpighian tubules. The first volume is nut yet completed, 

 but the 800th page lias been reached and the 1000th figure. 



* Journ. Exp6r. Zool., v. (1908) pp. 311-26 (1 pi.). 



t Zool. Anzeig., xxxii. (1907) p. 1. 



X Gli Insetti, Milano, 1908, pp. 713-800 (1 pi. aud figs. 892-1000). 



