MARINE FAUNA AND FLORA OF SOUTH DEVON AND CORNWALL. 87 



dages : at a later stage in the develojiineut the posterior pairs of pereiopoda 

 are developed with secondary appendages like the Lobster in its primary 

 stage. At this time the resemblance to some of the Mijsidce is so great that 

 it is highly probable that some of those Mysidce that are distinguished by 

 the development of their appendages in the form of true legs may he only 

 the young of the several species of Crangon. 



Pcdcemon. 



The larva of the common Prawn differs but little from that of the Shrimp 

 in the early stages of its development. The chief points of distinction arc 

 only such as could be called specific, and not improbably may be found in the 

 young condition of the larva of various species in either genus. They chiefiy 

 exist in Palcemon, having a longer rostral spine and a dorsal spine being pre- 

 sent on the posterior margin of the fifth somite of the pleon. 



It would be interesting, should we have the opportunity, to compare the 

 larva of the enormous freshwater Prawn of Guatemala, a crustacean as large 

 as a half-grown Lobster, with that of our European species. 



Palinurus mannus. 



In my last Report are given figures of the young of the genus Palinu- 

 rus, an animal that has excited considerable attention amongst carcinologists 

 in consequence of its near resemblance to the form of Phyllosoma, a circum- 

 stance that has induced many zoologists to believe that they arc but the same 

 animal in different stages of growth. Since the presentation of the second 

 Report, in which I gave certain reasons for not too readily accejiting this con- 

 clusion, Dr. Anton Dohrn has given much time to the subject, and traced the 

 development of the ovum from the commencement to the period when the 

 j-oung animal quits the egg-case. He writes to me from Messina, February 

 1869 : — " I only assure you that the thing is finished. The Phylhsoma are 

 the larva3 of the Loricatcv. I have followed the development of Scylhirus and 

 Palinurus eggs, and both have brought out Phylhsoma. What is there so 

 anomalous in Phyllosoma ? It is nothing but a depressed Megalops. ... I have 

 followed the development of the interior organization as well, and there is no 

 dift'ercnce of real value between Phyllosoma and Scyllarus, or Palimirus." 



This, which gives the author such confidence, is nothing more than has 

 been known for the last twenty years. The question is not as to the forms of 

 the larva of Palinurus, Scyllarus, &c., but whether certain animals that are 

 like them, but five hundred times as large, that we find mostly in exotic seas, 

 are the same but a little older specimens. If they arc, as Dr. Dohrn and 

 other naturalists afiirm, then they establish the remarkable fact that the larva3 

 of these Crustacea grow from the one-tenth of an inch in length to that of 

 one or two inches in length, without any material variation of form, a 

 feature that is not consistent with the life-history of the development of the 

 animals of this class. 



If we examine the progressive growth of other Crustaceans, we find that 

 with every increase in growth there is a fresh moult, and every moult de- 

 velopes the animal a stage nearer the tyjie of the adult animal. If the 

 Phyllosoma be, as contended, the young of Palinurus, then an arrest in pro- 

 gressive development takes place, while that of growth continues. 



An argument in favour of this being the case (that Phyllosoma may be the 

 young of Palinurus) may be found in a species described by De Haan in 

 Siebold's ' Fauna Japonica ' under the name of Ph. Guerinii, in which an 

 intermediate progressive step exists, inasmuch as the carapace is developed 

 so far posteriorly as to cover the pereion. 



