100 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Plate IY. 



Fig. 1. Longitudinal section of a single ommatidium. 

 (Drawn with the camera lucida.) [ace. con.) 

 accessory cone ; (b.m.) basement membrane ; 

 (con.) cone; (corn, cut.) corneal cuticula ; (nuc. 

 con.) nucleus of cone cell; (nuc. ret.) nucleus of 

 the retinular cell; (op. n. f.) optic nerve fibre; 

 (pg-) pigment; (pg.c.) pigment cell; (ret.) 

 retinular cell; (rh.) rhabdomere ; (s-c. hyp.) 

 sub-corneal hypodermal cell. 



Fig. 2. Transverse section of ommatidium showing the 

 six retinulae cells and their rhabclomeres. 



Fig. 3. Longitudinal section through the cuticle of a 

 segment of the flagella of the second pair of 

 antennae to show a sensory bristle and its 

 nerve supply. (ch.) thick layer of chitin ; 

 (ctla.) cuticula; (hyp.) hypodermal layer ; (n.f.) 

 nerve fibrils ; (s. b.) sensory bristle ; (sh.) sheath 

 of sensory bristle. 



Fig. 4. Generative organs of the male. (t.) testes; 

 opening into (v.d.) the vas deferens, which 

 opens externally by the styliform appendages 

 (st. ap.). 



Fig. 5. A collection of ' sperm-colonies ' as they are 

 found in the vas deferens, in the cohesive 

 substance secreted by the latter. 



Fig. 6. Early stage in the development of the egg, 

 showing the cleavage of the germ disc into the 

 two antero-lateral mesoderm fundaments (a.m.) 

 and the median posterior endoderm fundament 

 (end.). 



Fig. 7. The ' nauplius ' stage of the development of 

 Ligia, showing the three naupliar appendages. 

 (l.a.) and (2.a.) the first and second pairs of 

 antennae, and the mandibles (mand.) ; (end.) 

 endoderm fundament ; (f.z.) formative zone ; 

 (op.) optic lobe. 



Fig. 8. A later stage in the development, showing the 

 elongation of the formative and the formation 

 of appendages, also the rudiments of the 

 ganglia, (an.) anus ; (1. and 2. mx.) first and 

 second pairs of maxillae; (map.) maxillipedes. 



The last three figures are after Nusbaum. 



