266 BULLETIN OF THE 



Edwards (No. 12, see p. 268) records a monstrosity affecting the eye- 

 stalk of Palinur us penicillatus ; and finally Packard (No. 17) has noticed 

 a deformity of the caudal spine of Limulus Polyphemus. The last is 

 probably not so rare as Packard supposes, as I have found two specimens 

 of Limulus with similarly deformed spines. There is also in the Museum 

 of Comparative Zoology a small deformed specimen of Limulus Polyphe- 

 mus, in which the left side of the gill-bearing segment of the body is 

 marked by a deep concavity and absence of the lateral spines. Further, 

 Figs. 2 and 8 on Plate II. of this paper portray deformities of other parts 

 than the great claws. Fig. 2 represents a monstrous condition of one of 

 the small chelipeds of the lobster, and there is another specimen in the 

 Museum in which the index or immovable finger of the chela of either 

 the first or second pair of legs is double. Another lobster presents a de- 

 formity of one of the third pair of maxillipeds, the terminal segment 

 being divided into three lobes. Plate II. fig. 8 represents a deformed 

 lateral spine of the carapace of Callinectes hastatus. 



Reviewing all the deformities which have been described among Ar- 

 thropods, I would divide them into five categories, as follows. 



Deformities : — a, of deficiency. 



b, of excess. 



c, of transformation. 



d, of arrested development. 



e, of hermaphroditism. 



a. In individuals affected with deformities of this class, certain parts 

 normally present are wanting. Among Crustacea such cases are, as far 

 as I am aware, never congenital, but result from accidental amputation 

 of parts commonly restored by new growths, as before observed. 



b. Monstra per accessum. Under this head fall the majority of the 

 monstrosities that have been described among Arthropods. Among 

 insects the numerous cases recorded by Asmus,* Mocquerys,f various 

 contributors to the Annales de la Societe Entomologique de France, and 

 lately by Jayne,J etc., etc., for the most part belong here. In these 

 cases it is commonly the antennae and legs which are the seat of the 

 monstrous developments, which usually take the form of a duplication, 

 or even triplication, of the appendage. In most cases such double or 

 triple appendages are single at the base, the duplication or triplication 



* Monstrositates Coleopterorum, 1835. 

 t Eecueil de Coleopteres anormaux, 1859. 



% Descriptions of some Monstrosities observed in North American Coleoptera, 

 Trans. Amer. Ent. Soc, VIII. p. 155, 1880. 



