70 Miscellaneous. 



4. However the larvae of various species of Crustacea may resemble 

 each other in external form, nevertheless in the arrangement, the 

 form, and the number of the spots of the skin and intestine, and 

 especially in the number and conformation of the provisional appen- 

 dages which adorn the extremity of the last segment of the abdomen, 

 they present definite characters which enable us to say to what 

 species any particular larva belongs. 



5. The stomach of the larvae of the marine Crustacea presents 

 no solid piece adapted to the grinding of food ; it is merely furnished 

 on its inner face with rigid spinules arranged in rows, and with vibra- 

 tile cilia like those found in the stomachs of a great number of the 

 lower animals. These cilia communicate an incessant movement of 

 rotation to the organic molecules upon which the animal feeds. 



6. In all larvse of Crustacea, the liver, at first reduced to two 

 simple cseca, one on each side, is manifestly a diverticulum of the 

 intestinal tube, with which it has wide communications ; by ramify- 

 ing, it forms a hollow tree, at the base of which we may see oscillating 

 the vitelline globules which the umbilical vesicle pours into the 

 pyloric portion of the intestine. 



7. The marine Crustacea, however the respiratory functions may 

 be ultimately performed, all have a tegumentary respiration in the 

 larval state. 



With the exception of the Lobsters, which, when first hatched, 

 have a rudimentary branchial apparatus quite unfit to perform any 

 functions, the larvae of the other genera of Crustacea enumerated 

 above are absolutely destitute of this apparatus ; some, indeed, do 

 not present any traces of it until after several moults. 



8. The want of the function of branchial respiration necessitates 

 a radical difference between the circulation of the individual in the 

 larval and the individual in the perfect form — that is to say, having 

 acquired branchiae. In all the larvae of Maia, Porcellana, Crangon, 

 Palcemon, Palinurus, Homarus, Cancer, &c., the blood which the 

 arteries have distributed to the different parts of the body returns 

 entirely, directly to the heart, and this condition persists for a con- 

 siderable time. It is only after the third moult, in the most perfect 

 larva of the species inhabiting our seas — that of the Lobster — that a 

 few globules are diverted from the original general circulation to 

 penetrate into the nascent branchiae. 



9. All the arteries open directly into the venous passages by an 

 aperture more or less bevelled and more or less dilated into a trumpet- 

 like form. 



10. In some larvae the abdominal artery may present a sort of 

 sphincter in its course, at some distance from the central organ of 

 circulation ; this, by contracting, temporarily suspends the flow of 

 blood to the hinder parts*. 



* This remarkable peculiarity exists not only in the larvae of the Lob- 

 sters, as already indicated, hut also in those of the Porcellance. It is even 

 probable that it will be found in many species, and perhaps in all ; for 

 when we observe the circulation in the last segment of the abdomen of 

 larvae of Cancer, Careinus, Palcemon, he, interruptions are perceived in it. 



