386 



COMPARATIVE ANATOMY 



CHAP. 



We thus again see that in the Copepoda also the body with its limbs becomes 

 progressively differentiated from before backward. Inasmuch as all the limbs of the 

 adult animal are fully and typicalty developed, w T e find in this case, during the 

 development, no reduction of limbs once (i.e. in larval stages) strongly developed. 



Development of Sacculina (Order Cirripedia, Sub-order Rhizocephala). 



The comparison of the process of development in free-living Entomostraca with 

 that in the parasitic forms is very instructive. Let us take that Crustacean form 



FIG. 259. Various larval stages of Sacculina Carcini. A, Nauplius after the first moult. B, 

 Cypris stage from the side. C, The same, 3 hours after the larva has by means of its adhering 

 antennae attached itself to a seta of the host. D, Formation of the Kentrogon larva. E, The 

 same completed, the Cypris larval shell thrown off. F, The arrow has bored through the chitinous 

 carapace of the host. The contents of the sac begin to pass into the body cavity of the host through 

 the arrow, fs, frontal sensory organ ; ua, Nauplius eye ; gl, glands of the frontal horns ; ov, rudi- 

 ment of the ovary ; /, fat globules ; &, seta of the host, to which the parasite has attached itself by 

 means of its adhering antennae ; pf, arrow of the Kentrogon stage ; ab, abdomen (after Delage). 



which in an adult hermaphrodite condition is the most degraded and deformed, viz. 

 Sacculina (Figs. 208, 248). Although the adult animal cannot be recognised as a 

 Crustacean, the series of larval forms through which it passes during its individual 

 development most clearly proves it to be such, and related to the Cirripedia. 



Nauplius Stage (Fig. 259, A}. A typical Nauplius with its 3 characteristic pairs 



