ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 689 



small Octopus, with branched processes scattered over the body, which the 

 author names Polypus arborescens sp. n. A very striking peculiarity 

 is the preponderance of Octopods as compared with Decapods. The pecu- 

 liar, possibly protective, papilla on Polypus arborescens are described at 

 length, but their nature remains somewhat enigmatical. 



£• Gastropoda. 



Senility in Gastropods.* — Burnett Smith makes a suggestive con- 

 tribution on this subject. In the last whorl, or in the last few whorls 

 of many Gastropods of different groups, there are characters of senility. 

 They are the last characters which occur on the shell, and foreshadow 

 the death of the individual. " Senile species or genera of fossil Gastro- 

 pods never transmit descendants to later geologic formations, but 

 represent the end members of short branches on the phylogenetic tree." 

 The rate of evolution varies greatly. " The forms in which the evolu- 

 tional rate is rapid are bizarre senile offshoots." An accident to an in- 

 dividual may bring about a sudden appearance of senile characters, which 

 are sometimes "extra-specific" — i.e. found in some senile offshoot from 

 the same stock. Unequal acceleration of characters seems to be a 

 common phenomenon, and features which occurred at the same time 

 in an ancestor are apt to be widely separated in the ontogeny of a 

 descendant. 



Habits of Tortoise-Shell Limpet, f — M. A. Willcox describes the 

 life and habits of Acmc&a testudinalis. The size seems to be correlated 

 not necessarily with a low, but with an equable temperature. In autumn 

 they seem to retire a little below tide-mark. The fastest crawling 

 observed was about three inches per minute. There is presumptive but 

 inconclusive evidence as to a homing habit. The food is exclusively 

 vegetable. In certain circumstances atmospheric air may be respired. 

 Evidence of the perception of light and darkness, of a temperature sense, 

 and of great tactility, is adduced. The tentacles, the gills, and the whole 

 body surface are tactile. The ovary, when ripe, has a crushed-strawberry 

 colour, and the testis is golden brown ; otherwise the sexes are alike. 

 The eggs are imbedded in a layer of mucus. There is some inconclusive 

 evidence that fertilisation is internal. The only enemy discovered was 

 the dog-whelk, Purpura lapillus, which sometimes bores the shell. 



Breeding Habits of Chitons.! — H. Heath gives some notes on 

 these from the Californian coast. In Ischnochiton mertensii, I. cooperi, 

 Mopalia mucosa, and Katharina tunicata, egg-laying does not take place 

 until the sperms have diffused into the neighbourhood of the females. 

 Trachydermon raymondi carries its eggs (to the number of about 200) in 

 the mantle cavity on each side of the foot until they reach an advanced 

 trochophore stage. While the gills are thus covered and respiration 

 impeded, the proboscis is highly distended with blood, and the lateral 

 protuberances (" Laterallappen ") become much enlarged, and both may 

 temporarily assume increased powers of respiration. When the young 



* Proc. Acad. Sci. Philadelphia, 11)05, pp. 345-61 (2 pis.). 

 t Amer. Nat., xxxix. (1905) pp. 325-33. 

 % Zool. Anzeig., xxix. (1905) pp. 390-3. 



Dec. 20th, 1905 3 A 



